Yeah dude that makes no sense. She probably thought you were afraid to touch her, honestly.
First of all, how would you know that you give the best massages? Have you gotten massaged by every dude and lady around? Even if you have, you can't have massaged yourself, so how would you know that yours are the best?
Try being as serious and matter-of-fact as you can. Say: I wanna give you a massage. Then do it.
Joking is fun but seriousness is sexier in my opinion, when you're being seriously sexual. If she seems nervous, THEN joke, if you want. But don't be afraid of being creepy or sexual. You have to learn sometime. Risk being creepy. You want the vibe to be SEXUAL, you want to be touching her and having her go unhhh, not joking with her and having her go hahah. Although ideally some of both is good.
And.... DON'T try to impress her. You will impress her BY NOT TRYING TO IMPRESS HER. If you give a good massage, go ahead and massage. If you don't, then go ahead and ask her to help you learn. Don't feel like you have to be some omnipotent dude who magically knows how to give massages =P. The fact that you're alive, healthy, and on a date with her is plenty enough.
Was your heart beating really fast and you felt terrified that she was gonna walk out on you at any second or call her friends and say "what a creep"? If so, that's fine... You still should have sat down next to her, put your arm around her, and cuddled with her like you wanted, though. You shoulda looked into her eyes and smiled and lingered over her lips with yours, brushing lips, drawing out the tension... Or whatever your body really wanted to do with hers. Don't trust your stupid brain. Listen to your body and how it wants to get close to her. Do what it says.