Wow, are you sure its really 3 minutes? Did you seriously time it?
The thing is I guess its a different sensation when your fucking than jacking off, that is probably why you are done in 3 minutes.
I suggest to have good amount of practice, I mean seriously if you are having sex with extremely hot girl then it is not very easy to contain yourself. Try thinking of something or picturing something else. Focus your attention on other things, if you think you are going to be done, try pulling it out and do something else, besides, there are other spots to make the girl perfectly happy. just find your pace, and you will be okay.
Somehow 3 minutes is a record breakign number. I can only do that if i have not been laid for like sooooo long. :)