C in Microbio what should I do?

So I’m currently taking microbio and it’s genuinely kicking my ass. The first test i got 71 then got 67 then yesterday I got a 50. I still have one more and he drops the lowest but I don’t what to do. I can possibly get a B but I don’t know. This professor is genuinely hard like the average for all the tests are failing and I am trying so hard right now. I currently have a 3.8 something and I am also taking 5 classes along this one with As. Should I be worried and not being a competitive applicant anymore? I still need AP2 and Gen chem. What should I do?