Don't worry my friend, tell her you weren't ready yet.
The next time you get intimate, start off with roleplays then finish off with the lights off. She won't see a thing literally
I dated a guy that was about your size. The size def doesn't matter. Sex is mostly a mind thing anyway. If you're really attracted to the guy because he's sexy and fun and intelligent (or whatever attracts a particular girl) then it won't matter at all. Too bad that she may miss out.
I was married to a guy with a big penis and sex honestly sucked. I divorced him and my new boyfriend has a smaller penis and the sex is incredible. Sex has a lot to do with your passion for each other. I didn't have passion for my ex husband.
I agree with Anahi.
If she really cared about you, it wouldn't matter to her.
It's like a guy not going forward with a girl sexually because she's an A cup.