Your chances of doing well as a biology major or premed student definitely will not be "extremely hurt " by your decisions around AP classes. The background in biology from an AP class will likely be helpful, but not required. It will not make or break you. In your last year of high school, try to maintain your high gpa, keep doing your extracurriculars, and remember that college applications take a lot of time so don’t overload yourself academically. If you struggle in chem or bio, I would actually take the one that’s harder for you. If you are a pre med student in college, you’ll have to take them both and the preparation you get from an ap will be helpful. Think of it this way: it’s better to get a lower grade in high school than in college, medical school will heavily weigh your college gpa as a part of the admissions process, and your high school gpa will have little to no bearing. I took ap chem, my senior year because chem is really hard for me and knew I would need it in college. I excelled in chem my first year in college, and the first semester was basically a review.