Afraid

I feel so bad. I've been with my girlfriend for a while and we have never had sex. We have talked about it and I told her I was ready. She wasn't so we waited a few weeks and now she is. I'm terrified now that she wants to because I don't like being touched down there and I don't know how to tell her. I feel like she would think I'm just taking advantage of her. I love her so much and I honestly think that she will be my wife one day. Am I selfish. Should I just let her do it. I want to have sex but not the say she does