Stay home.
Serious answer: use it to your advantage. Being anxious about a gig means you care about it. Consider the alternative.
So if you care about it...it's going to be a great experience, one way or the other...maybe a "learning" experience(
) or a major league I'm a god ego-fest(
)...
Other suggestions:
Keep it brief.
Don't talk a lot, just play.
Practice, like Frayne said...but don't beat yourself up if you flub something...people hardly notice unless they notice you noticing.
The best possible practice is putting yourself out there, on the line, in front of people.