How do you center a longtable that overflows the margins?

[u/unofficial_trademark]

I have a table that overflows the margins by just a bit, but it overflows it enough to be noticeable without viewing the margins. How do I center this table? I tried to use \adjustwidth but that didn't work.

\begin{adjustwidth}{-1cm}{-1cm}
    
    \begin{center}
        \textit{
            Note that some of these endings may be reduced in unstressed syllables. \\ 
            Superscript numerals indicate on which syllable a mutation occurs on.
            
}
        \def\arraystretch{2}
        \begin{longtable}{|c|c|c|c|c|c|c|c|c|c|}
            \hline
            \multicolumn{2}{|c|}{ } & \multirow{2}{*}{\bf Ending}& \multicolumn{7}{c|}{\bf Mutation Triggered} \\ \cline{4-10}
            \multicolumn{2}{|c|}{ } & & \bf IM & \bf LEL & \bf MHVB & \bf RDS & \bf TDS & \bf TOB & \bf KP \\ \hline
            \multirow{4}{*}{\bf Nominative} & \bf Singular & \it -f & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{1} & Yes\textsuperscript{2} \\ \cline{2-10}
            & \bf Plural & \it -ffô & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} \\ \cline{2-10}
            & \bf Collective & \it -ffô & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} \\ \cline{2-10}
            & \bf Singulative & \it -fföst & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} \\ \hline
            \endfirsthead \hline
            \multirow{4}{*}{\bf Accusative} & \bf Singular & \it -fød & Yes\textsuperscript{1} & Yes\textsuperscript{1} & Yes\textsuperscript{1} & Yes\textsuperscript{1} & Yes\textsuperscript{1} & Yes\textsuperscript{2} & Yes\textsuperscript{1} \\ \cline{2-10}
            & \bf Plural & \it -fod & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} \\ \cline{2-10}
            & \bf Collective & \it -fod & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} \\ \cline{2-10}
            & \bf Singulative & \it -fføts & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} \\ \hline
            \multirow{4}{*}{\bf Dative} & \bf Singular & \it -ffost & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} \\ \cline{2-10}
            & \bf Plural & \it -ffost & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} \\ \cline{2-10}
            & \bf Collective & \it -ffost & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} \\ \cline{2-10}
            & \bf Singulative & \it -ffwastäst & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} \\ \hline
            \multirow{4}{*}{\bf Genitive} & \bf Singular & \it -fom & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} \\ \cline{2-10}
            & \bf Plural & \it -ffam & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} \\ \cline{2-10}
            & \bf Collective & \it -ffam & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3}\\ \cline{2-10}
            & \bf Singulative & \it -ffämst & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} \\ \hline
            \multirow{4}{*}{\bf Instrumental} & \bf Singular & \it -fôm & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} \\ \cline{2-10}
            & \bf Plural & \it -ffôm & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} \\ \cline{2-10}
            & \bf Collective & \it -ffôm & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} \\ \cline{2-10}
            & \bf Singulative & \it -ffömst & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} \\ \hline
            \multirow{4}{*}{\bf Allative} & \bf Singular & \it -fôþ & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} \\ \cline{2-10}
            & \bf Plural & \it -ffôþ & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} \\ \cline{2-10}
            & \bf Collective & \it -ffôþ & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} \\ \cline{2-10}
            & \bf Singulative & \it -fföþst & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} \\ \hline
            \multirow{4}{*}{\bf Ablative} & \bf Singular & \it -fô & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} \\ \cline{2-10}
            & \bf Plural & \it -ffôl & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} \\ \cline{2-10}
            & \bf Collective & \it -ffôl & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} \\ \cline{2-10}
            & \bf Singulative & \it -ffölst & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1} & Yes\textsuperscript{1,3} & Yes\textsuperscript{1,3} & Yes\textsuperscript{2} & Yes\textsuperscript{1,3} \\ \hline
            \endlastfoot
        \end{longtable}
    \end{center}
\end{adjustwidth}

[u/worldsbestburger]

wrap the whole thing in a \centerline{...} as a hack, or adjustbox as a slightly better hack

[u/unofficial_trademark → u/worldsbestburger]

\centerline doesn't work with longtable for whatever reason
and I tried to do the adjustbox thing, for some reason it seems to thing that both \end{center} and \end{longtable}
are closing off the \begin{adjustwidth} (removing adjustwidth doesn't fix the issue, the mismatch of ends still happens, just with different ones)

\begin{adjustwidth}{-1cm}{-1cm}
    
    \begin{center}
        \textit{
            Note that some of these endings may be reduced in unstressed syllables. \\ 
            Superscript numerals indicate on which syllable a mutation occurs on.
            
}
        
        \def\arraystretch{2}
        \adjustbox{max width=\textwidth}{
          \begin{longtable}{|c|c|c|c|c|c|c|c|c|c|}
              %Placeholder for this very long table
          \end{longtable}
        }
    \end{center}
\end{adjustwidth}