BibTeX has several entries like @masterthesis and @article as well as several fields. The Type has to be defined for mastersthesis, otherwise, it will say "Unpublished Master's Thesis", when using APA style

\bibliographystyle{apacite}

This is also discussed in the MSthesis-ProQuest-Cite Repository.

If the box is overfull and LaTeX document goes into the edge space, then enable sloppy mode, as in:

\begin{sloppypar} % avoid paragraph being too long and spill over next line.
This text is very narrow and has a long number in math mode, \SI{12.4132 x 9875.232}{\nano\meter}.
\end{sloppypar}