To be perfectly honest, nervousness doesn't bugger girls all that much.
If you don't know what to say, that's okay.
Just don't doubt yourself.
...(Err, edit, because if you doubt yourself, she will doubt you)
You sound pretty cool, and as an autie/aspie you have no choice but to "be yourself" : )
And if a certain girl doesn't like you for who you are, you don't want them, really.
But to be honest(yes, again), most girls like sincerity more then self-control... Only slightly more:p
Know yourself, and just relax. And if instinct sets in, c'est la vie. If anything, it's a compliment to her level of attractiveness..heh.
Good luck.