Sounds like you're going from zero to 60.
Can you get and sustain an erection long enough to climax during mutual masturbation or oral sex?
If you don't know or you haven't tried, then try.
Because if it's nerves, then you may feel more comfortable if you get more used to being naked with her., and orgasming with her.
And don't forget that you're new to this. You can't expect to have perfect moves.
And that's okay.