Here we go, advise is cheap, But I spent a lot of money or this advice.. In my younger years I used to do a lot of public speaking, and I have taken quite a few courses on it. First it is ok to be jittery, it's actually good, it helps you to get prepared, I bet you are practising llike crazy... Second don't be to tough on your self, if you make a mistake just keep going, less than 5 % of you audaince is going to know any thing about music, never mind the guitar. ( You are the expert). When you look at the audiance, look at them as if they owe you money.. That puts them on a different level in your brain.. Lastly have fun... This will be a great time for you to remeber no matter what happens....

Good luck....