You've got the music as good as you're going to get it, you say? Friend, you
never get it as good as you're going to get it! I'm sure even a virtuoso musician would tell you that.
Regarding stage presence, well you've either got it or you haven't I'm afraid. And it's something you'll never be able to tell yourself; others will tell you, though, so just rely on them and believe what they say.
Overconfidence is ugly, though, and an audience will spot it a mile off. The effect is that the crowd actually end up willing you to fail - that's the price of being cocky.
Is this your first gig? The best advice comes from Tony Bennett, who was very nervous approaching his first show. He went to see Frank Sinatra who assured him that if an audience can see the performer is nervous, they warm to him/her all the more. If you're nervous, it means it matters to you.
Never stop being nervous