I used to get really nervous before I played shows because I was always worried that I would screw up. And I have screwed up many-a-times (sometimes worse than others) But you just have to accept the fact that it's going to happen. These days I still get nervous but not as bad as I used to. Something that helped me was not to look at the crowd, just focus on your hands. Eventually you just get less nervous and it just becomes part of the thrill of performing...and this just takes longer to happen for some people. So I think you just need to keep doing it.

This is the way I see it:

Whenever people see someone else that is nervous on stage they can tell. They know that it's hard to play when your nervous and know that person is probably much better players off stage than on. People aren't going to think your a bad player because you made a few mistakes on stage. Plus half the time they don't even notice. Also, there's always next time to show them different if they do notice.

Even the best players have bad shows.