It would certainly help to know which state you're in. Reaching top 5 in Ohio is very different from top 5, say, Tennessee (not that TN is super uncompetitive, but it's definitely middling).
If I want to get top 5 in my states, how should I study? This is my first year, and I really wanna do well.
I would suggest studying from the Excretory, Cardiovascular and lymphatics chapters from a high school Anatomy and physiology textbook like Marieb. a local high school library would lend you one if your school doesn't have it.