Unprotected sex

So my boyfriend and i had sex yesterday but not for long but im guessing there was a little pre cum. And i know pre cum can get you pregnant but last time we did it the same thing (which is only a few pumps i think that how u say it) and i didn’t get pregnant and got my period. Im 17 and in school i have no time to get plan b and i don’t have enough money to buy it. What should i do?