People. Why am I such a wuss when it comes to women?

I long for a girlfriend and only had one romantic relationship and that was years ago. I met this girl recently I really like and we get on - tho only known her for three weeks - but I think I do not give off the sexy vibe. She is gorgeous, short and curvy - in all the right places. I am tall but quite fat. She told me the other day I was 'so cute'. I think I have a good looking face. I responded by saying 'you are gorgeous but I think you seem like a heartbreaker - she said why? I said 'look at you' and she is a great dancer. The thing is I know it always comes off as wimpy. I try to say cute things and make them laugh. I am always polite and offer to buy drinks and open doors and even apologise and ask a girl are they okay if they bump into me! So I just wondered how to change myself to be more of the bad *** guy wome want sex from. Suggestions?