Hi there!
First off, I would like to emphasize that a single exam score is not indicative of your intelligence and you should not let it deter you from pursuing medicine. These are extremely stressful times, so it’s important to cut yourself some slack and forgive yourself. Maybe it’s some consolation that most premeds have a class that they struggled with or an exam that they failed, I myself can attest to this. 
Now, for some advice. I’d first suggest that you re-assess your study habits/methods. I’m going to link some previous Q&As that detail different study recommendations from other premed advisors: [1] and [2]. You could also join an SLC study groups/peer tutoring may be helpful as well because you can gauge what other kids are doing to study and you’ll have access to extra practice: SLC link. Alternatively, if you have tried the methods listed, I would recommend meeting with your professor and discussing study methods and ways to improve! Professors are usually open to meeting with students and discussing concerns, don’t be afraid to reach out. On a side note, in my past experience, Bio 172 allows you to drop your lowest exam score!
Just to reiterate, a bio exam is not indicative of your ability to pursue the pre-med path and many people are/have struggled with Bio 172. If you’d like to speak with further advisors on this matter, feel free to drop in our advising hours (Zoom link under the peer advising tab). I wish you all the luck!