Stage freight. :( I'm sorry.
All I can really tell you is what helps me:
I get some nerves sometimes(esp at things like auditions). For that, I play a mental game with myself.
I don't think about messing up, being good or bad, or how nervous I am or should be.
I think about making music. I say to myself "I know what I can do, so I'm going to do it and make music out of it" not "I'm going to play this and this and this in this manner so that it will be right." Even if it's wrong, make it music!
That's what it's about, anyway, when I think about it in retrospect.
Get in the jazz, as the line goes.
Hope that helps.
Good show.