You'lle never know unless you go Homeless:)

Sounds like you are suffering from the FEAR (F**k Everything And Run) Factor! That fear will disappear (mmm, that rhymes!) after the first verse of your first Song.
Being nervous isn't a bad thing imo. As Bill says, it shows you care:)
Maybe think about playing the Guitar you are comfortable with playing then if you like doing the stage thing then buy a new one. Of course if you are looking for an excuse to buy yourself a new Guitar...none better than a Gig!:)
I have a feeling you will do just fine. Just go up there and take a couple of slow, deep breaths before you start to play...*smile* I wish you every success and may this be the first of many performances for you.
Warmest Wishes,
Jude ( who bets Homeless will blow them away and will finish the evening wanting to play to Folks again..asap! :)