It's theoretically possible, if your urination didn't remove all the sperm from your urethra, or if there is a part of the duct where the sperm comes into the urethra that is not subject to the action of urination but does get the action of the fluid from the Cowpers gland. (I don't know the answer to this latter question but it should be easy to look up an anatomy chart and try to figure it out.) But this would sure not be the easiest way to get pregnant -- in any given month, a couple actively trying to get pregnant will only have about a 20% chance, so it's not instantaneous even when sperm gets in. You just don't want to be one of the rare cases.
Meaning, as you know I'm sure, it is really a bad idea to pull stunts like this. You were naked, dry humping, and you inserted the tip of your penis for 10 minutes. A woman can get pregnant from this. If your girlfriend wants to be able to keep claiming she's a virgin, she would be well within her rights to tell you to go to hell when you ask to do this. (Or if she is unconcerned about whether she is a virgin or not, and is as eager as you, she should get on the Pill or an IUD, and not do anything without a condom.) Birth control was invented so horn-dog boyfriends don't become accidental daddies. Please remember how worried you are now next time Mr. Johnson gets excited, or sooner or later you *will* become a daddy unplanned, and that is a whole new ballgame.
Be careful and be mindful of your body and the female body. The warm sensation she felt could have been her own fluids. Pre-*** does have sperm and can make a woman pregnant. If I were you guys I wouldn't continue such activity until you are ready to face the results. Good luck guys