You are thinking about it too much. PE is more often than not psychological depending on your age. Relax, don't be nervous, and fuck her slow and steady. Talk to her, let her know that you want to try to make it last. When my girlfriend and I first started fucking it was like that with me too, and she worked with me to make it better. Penetrate her missionary, and then instead of thrusting, lean forward and make out with her, massage/kiss her neck and breasts. Don't thrust at all, or at least as little as possible. It'll get your penis used to the sensation of being inside of her pussy. Just make sure to lean back and rub her clit from time to time, otherwise it'll be nowhere near as enjoyable for her as it is for you :-P.
Then, when you make her cum, and it's time to make yourself cum... do it however you want. I normally wrap my hand around her neck and spit directly down her throat. Then I fuck her pussy mercilessly until I pull out and spray her face with my spunk. Then I throw I call her a filthy cunt and walk away.
Works wonders man.