Can i get pregrent the day before my period if my boyfriend pre-cums inside me?

Doubful: Any couple who have intercourse without contraception can get pregnant. That being said, the timing you describe would make it very unlikely.

Risk: Timing makes it unlikely. Pre-ejaculate may contain large amounts of viable sperm, smaller amounts of sperm that are dead or alive or no sperm. Thus, there is potential for pregnancy with pre-ejaculate. Sperm need to be deposited in the vagina or at the introitus for pregnancy to occur. Use protection every time you have sex if your are not ready for pregnancy.