First time having intercourse

7/3/12 Yesterday, my girlfriend came over and we messed around. She took off my pants and she took off hers. We messed around. I am terribly scared at this moment. Before I got the feeling of any semen coming I took out my penis. And ejaculated on the bed. Is there any chance that the slitest bit of semen might have gone threw and that cause her to get pregnant. I am terribly scared and I need an answer. What might the odds be of her getting pregnant ? Thank you.