If you are worried about playing sports in class, practice at home. You won't become an all-star player overnight, but you'll feel more comfortable (and look better) playing basketball in gym class if you've dribbled a few times beforehand. The same goes for any other athletic activity. Even jumping jacks can be difficult if you've never done one. When you're thinking of what to wear to look good in gym class, the goal should be to bolster your confidence. Thinking positively and dressing well create a self-confidence loop of sorts that will help you get through gym class more easily. You'll feel confident because you look good, and you'll look better because you carry yourself confidently. Staying focused on what you're doing will help you stop worrying about distractions. Your performance will improve, and you'll feel more confident as a result. Talk and bond with your classmates. Gym class is one of the few times you can interact with them outside of a classroom. Take the chance to set a relaxed atmosphere, and you'll realize people care less about your performance than you think. People are spending a lot less time looking at you than you think they are. Remember that except for the jocks, most of your classmates are nervous about gym class on some level too. Most of them aren't looking to judge you. Remember that gym class is one of the only chances you get to exercise in the day. Try to have fun with it.

Summary:
Try to learn the basics. Be confident. Relax and have fun.