I had an anal sex with my boyfriend but i don't know if i may get pregnant i'm scared?

No: No....you will not get pregnant via anal intercourse.

Unlikely: If any sperm entered the vagina during precum,and no condom was used,and you were in your fertile period, conception would be possible. Otherwise the odds against would be high.

Low risk: The risk of pregnancy following anal intercourse is low but not negative. It is advisable to use condoms during anal intercourse to decrease the risk of infections and never go from anal intercourse to vaginal without changing condoms. If you aren't ready for a baby, now is time to look into starting a reliable method of contraceptive regardless so you won't have this worry. Hope this helps.

Contraception used?: Did you use contraception(hormonal, IUD, implants)? If not, the sperm can egress from the rectum (Hershey Highway) and leak into the vagina afterwards and yes, pregnancy can occur.

Anal: Well first of all, always, always always use a condom with anal sex unless you want vaginal infections all the time. Second if it was unprotected and your partner ejaculated inside, it is possible for semen to come back out and get into the vagina. The best way to keep this from happening is to wear a condom and make sure it stays on until he walks away over to the bathroom.