My mid year report- help!!

Hello cc community,

So this is my course load for my senior year:
Ap psych, ap micro macro, ap bio, ap lit, ap gov, anatomy and phisiology, Multivariable calculus
I currently have an A in all of those classes except micro macro (A-) and now Multivariable calc (C+)
I’ve worked very hard in multivar, however our grades are determined by just the 4-5 tests we take per quarter and I haven’t quite adjusted to that grading system. I passed BC calculus with an A, but Multivariable is just a completely different monster that I’ve been unable to tame. My question is, how much will this hurt my college applications? I have to send in a mid year report and I’m very concerned, this is the first grade I’ve ever received that’s below an A-.
If it assists you in answering my question in any way, I am planning on majoring in biology and I also plan on taking some classes in philosophy and poli sci. I know your question is probably ‘why is she taking multivar calc then?’ Well, up until this point I thought I really enjoyed math and would go down the engineering path, but upon entering multivar in my senior year, I’ve changed my mind completely.
Also, I am hoping to get into a top tier university, brown and Dartmouth being two of my favorites.
Thank you!