I'm in the same predicament as you right now. I am trying to apply for a nursing program that accepts 96/1,000 applicants. So ever since I started my pre-req classes I feel like I am alway on edge. However, what I will say is that I have found myself freaking out a lot, and it all ended up to be nothing. I do feel like the stress help me keep motivated, and focused, but never ever let it consume you.
My advice to you is you keep those thoughts out your head, and stay focused on getting an A in this genetics class. Unfortunately we do get bad teachers sometimes, it's just how the system works. But try changing your study habits and techniques, and neve lose sight of your goals.
A sad reality about nursing programs
, is that the higher your GPA is, the better. A high GPA will never hurt your application. But if you have to take a B, then you that's okay too. Just make sure everything else are As! Best of luck to you.