Can I have reassurance :(

I had sex on Valentine’s Day and the condom broke. No, he didn’t cum. But I got a plan b just in case. I got my period a couple days after that (I was supposed to get it a week after Valentine’s Day but I assume the plan b made it come sooner) however, my cousin started making me freak out telling me that I could still be pregnant even though I had my period! I had a long, heavy, 5 day period. Could I really be pregnant or is my cousin absolutely wrong?