The scars don't matter. Even scars that are evidence of your insecurity (ie scars left by voluntary cutting) are much more important in your own mind than they will be to anyone else.
so please do not let yourself dwell on those or torment yourself by imagining what other people might be thinking.
try out for basketball. even if you don't make the team, you will have taken a step forward, and that is important for your sense of achievement.
Good luck. Things will not always be so difficult. It does get easier as you get older.