The only way to get over this feeling and fear is by doing things by yourself. It’s like a muscle that needs to be exercised. You’ve just been incredibly sheltered and don’t have much experience doing things alone.
A sports practice seems like the perfect opportunity to focus on the sport you love and not worry about having a chaperone. You will make more new friends going to things alone, anyway. They aren’t total strangers, right? They’re other students in your grade level with one thing in common- the sport. You can do this.