To be honest, I don't understand the idea of changing biology major to mathematics. As far as I know, this span is not difficult to understand. Regardless of the subject you took, it is the master's stage:

1. Your professional foundation will encounter great challenges, and the mathematics of biology specialty is definitely not enough to cope with the level of master of mathematics;

This kind of questioning may be discriminated by the teacher when you re-examine.

So I suggest another option.

PS: The above views are purely my personal views and are for reference only!