When it's up it's up! You can't really do anything about it.
So don't feel too bad. Just make sure you don't get cought, or you'll be sorry.
Let me ask you a question... Do you feel guilty for what you have done? If the answer is yes. Then you have learned from the experiance and try and say NO next time. I know that will be difficult when your Dick's on Hard mode.
If you don't feel guilty, then so be it! Fuck her again if you want, it doesn't really bother me, it's your life!