Take the courses/education that is only required. You can always expand upon it later. The hiring process is very long so it is best to start working and applying when you get the chance. If you can take extra classes while you are working, that would look great.
When you attend the police academy you will have a physical education and may not be doing things you like. Getting in shape right now is the best thing for you, but try to run often or get involved into some kind of sport or recreational activity. Some people lift up dumbbells a couple times and call it a day.
Best of luck to you! Also, I do not know what you mean by being "uncomfortable" in school but try to make the most of it. You will find yourself in many uncomfortable situations in law enforcement!