This is a problem that many athletes initially deal with, because they are afraid of messing up in front of their coach and everyone else watching. I would suggest talking to your coach and asking for his or her advice. Secondly, the main thing that I can tell you is that you have to trust your ability. You were good enough to make the team and can play well during scrimmages so try to think about the game situation as just another scrimmage. Play the game and don't focus on anything else going on in the gym. Soon, you will be able to realize that this was all just mental and that you have the ability and skill level to play just fine during the games. It may take a while, but you have to work at it. If not, your coach may stop putting you in the games.

just do wat u do

Rush yourself while practicing imagine everyone watching you, make yourself a little paranoid get used to pressure. you might go a little spastic to begin but I really think anyone who has played knows you cant just relax you have to learn to control your own game