Is Pregnancy Possible Despite No Ejaculation During Intercourse?

Hello. I've been pretty uptight about my girlfriend being pregnant. The only thing we've ever done that involved sex was when I put it in and humped her for about 30 to 45 seconds. I'm sorry for the incompitant-sounding method of explaining this. I never ejaculated, but I remember masturbating about 12 hours before. She, so far, has not really had any differences in anything, and it's been a week since we've done this. Again, I really can't think of any other way to explain this, so sorry for any immaturely sounded explanations.