I had sex around 4 am on 03/30 my boyfriend had came in me , my first fertile day was the day before on the 29th could i possibly become pregnant ?

YES!: I am not sure how you are determining your fertile days, however, if you were not using contraception of any kind and you had a positive test for ovulation ( lh surge), it is possible that you could become pregnant within 72 hours of that surge. See your provider tomorrow if you do not want to become pregnant

Absolutely.: Your timing could hardly be better for pregnancy.