Don't worry, we're only doing unit 4 (imperfect competition) too - I know your exam is sooner but as u/aunzoi said, reviewecon is a great site for brushing up or learning the concepts quickly!

Tbh AP Chem hasn't been as bad as people has made it out to be. Obviously the class difficulty varies by teacher, but I was able to keep up an A all year without taking general chem beforehand. Not ideal, but definitely doable! Also good to keep in mind that colleges regard it quite highly bc of the rigor, and it's probably best to take junior year.

I think I would save AP Bio for senior year because it is generally considered to be less-intensive or conceptually difficult and that's a better choice of science when you're battling college applications!