You know I think you just worked up the idea of having actual pentration with her so much that you could have gotten really nervous/excited and came too quick. Thats alright it happens to just about ever single man in their life at one point, take it as a learning experience and laugh it off!
Controlling your ejaculation takes a little bit concentration and practice that you can do on your own. A good method to try is to be able to spank the monkey for 15-20 minutes without cumming. Don't breath in your chest but in your stomach it is much more relaxing. Make such that you are relaxed! Tension will make you cum quicker. There are other techniques you can do like the one about strengthening your muscles. It's the same muscle you can use to stop urinating in mid stream, it's kinda like Kegal exercises for men.
I would recommend the book the Multi-Orgasmic Man, lots of good info in there, even some on getting your mate more comfortable to have sex.