I don't want to try out for high school soccer?

If they demand that you try out, just slack through it and make comments like "this is stupid" or "I hate soccer" where the coach can here you. Make sure you come in last, kick the ball the wrong direction, etcetera.

Or even better, talk to your parents. Do not tell them they are wrong about you being insecure. Ask them why they want you to play soccer. Ask if any other activities would be acceptable. Be ready to discuss why you don't want to play soccer, and what you intend to do with all your after school time until track.

There's a decent chance that they don't care about soccer, but they do want you to participate in some organized activity after school so you won't be idle and more tempted to get into trouble.

Then don't. They can't make you do anything you don't want to.

There is only one reason needed, you don't want to.

Don't do anything you don't want to do. If they're pressuring you, ignore their comments. Honestly, there's so much you can get involved in, and you already said you want to do something else. Get into the hobbies and activities that you like, and dedicate your time and energy to things that you're actually interested in.