Help with bibliography

[scienceshaina]

Hi all, I am using this template (which I love, thank you so much for creating it!) but the bibliography page just shows up completely blank. I downloaded my copy of the template a while back so it could be something with an update but I looked through the style sheet and main tex file and I don't really see any differences. In my version of the style sheet I have:

%% Fix the bibliography

\AtBeginDocument{%
\let\base@thebibliography\thebibliography%
\let\endbase@thebibliography\endthebibliography%
%
@ifpackageloaded{biblatex}{%
% Double-space the bibliography entries, according to an interpretation
% of the discussion at
% http://tex.stackexchange.com/questions/13742/what-does-double-spacing-mean
\setlength{\bibitemsep}{\baselineskip}%
% Add entry to TOC
\AtBeginBibliography{%
\addcontentsline{toc}{\toc@section}{\MakeTextUppercase{\bibname}}%
}%
}{%
% Add entry to TOC
\renewenvironment{thebibliography}[1]{%
\begin{base@thebibliography}{#1}%
\addcontentsline{toc}{\toc@section}{\MakeTextUppercase{\bibname}}%
}{\end{base@thebibliography}}%
}%
}

At the end of the main document I have:
\interlinepenalty=10000 % prevent split bibliography entries
\bibliographystyle{umassthesis}
\bibliography{sample} (my file is called sample.bib and I just switched out the contents of it to match umthsmpl.bib)

Also, just to note I'm compiling in Overleaf.

I thought maybe it was because the biblatex package isn't loaded so I added that in the load packages section of the .cls. When I do that it gives these errors at these lines:

\bibliographystyle{umassthesis} --> "Biblatex error: \bibliographystyle is invalid"
\bibliography{sample} --> "can only be used in preamble"

ETA- I fixed it. I kep the load biblatex package line in the .cls and got rid of the bibliography lines at the end of the main tex document. I replaced those two lines with \printbibliography at the end and \addbibresource{sample.bib} right before \begin{document}.

Thanks!