Had anal sex with my bf last night. he did not ejaculate, only pre ejaculate. should i be worried about getting pregnant?

Difficult to tell: I would not say exactly say you had to be worried, but I would not consider you 100 % safe. If you think this happened around your ovulation, take plan B and take a pregnancy test in a week - it takes the test a week to become positive. On a different note, if you engage in anal sex, tell your gynecologist. He/she may want to do an anal smear for anal dysplasia in addition to a pap smear.