wack it prior? soothing, gets rid of anxiety, hell, surgeons do it before dangerous and extensive surguries, there must be something to it!
I saw a kid who had the same problem as you, he puked right before they started playing, came back and RIPPED it up. after the show I made sure to go over to him, give him a pat on the back, and say "you play circles around me dude, you've got NOTHING to be afraid of!" and it brought some of the color back to his face, definitely cheered him up.
As for me, I started going to theater camp at age 10, so yeah, I'm more comfortable on stage than off it. just stick with it, if it helps, develop that rock star attitude to psych you up before hitting the stage.