Nervous about sex

Relax.... you'll be amazing!

What you should do is just go for it. Many guys are nervous the first time. And she probably knows not to expect much from you the first time.
With each time you do it, you get better and better. Just don't worry about it, and go for it.

If she truely likes you, she will be understanding. Just talk to her and tell her what you have just told all of us.