From my point of view, some flowers would be even better than chocolate. Here's why:
1. Since you aren't a couple or anything, they don't have to be fancy, or even roses (although roses = bonus points.) Just go to your local supermarket, get a small bouquet of different colored roses/other flowers for $10 or less.
2. Flowers are universal with girls. I am the biggest (straight) tomboy you will ever, ever run into, but even I;m a sucker for a nice bouquet of flowers. Hell, since its a first date you could even buy a single rose or whatever, and be totally in the clear.
3. Although I really, really like chocolate, I hate the fancy kinds that come in those nice boxes. When I want chocolate, I want a fucking Hershey bar, not fancy crap with stuff in it that gets in the way of...THE CHOCOLATE. Plus, if you aren't going to go expensive with the fancy stuff, chances are the quality will be pretty low.
Now, do bear in mind that this is just me (I have plenty of female friends who love those fancy chocolates. None who don't appreciate flowers though), so take it for what its worth. Just some food for thought.
And good luck! I hope she's cool, and that you have a great night tomorrow.