People make mistakes, drink fuelled, or balls-driven, spur of the moment mistakes. People fall for someone else, but still love the other person. Shit happens, but what you were planning was a real c*nts trick.
It seems that you don't respect her, so either man up and sort it out or fuck off and let her get on with her life with someone who does.
Foreplay, for many women, starts with conversation, compliments and feeling valued. If she is lacking in self confidence, then buying her a gym membership is not going to fucking help, (cue - so you think I'm fat, do you?) but talking to her, spending time with her, telling her she is beautiful and making her feel generally gorgeous may. It could take some time but if you do love her, then it would be time well spent.
.. she thinks it's virtually perfect.
I doubt that.