Plan B

So my boyfriend and i just had sex 3 days after i ovulated and we always use a condom and he came inside of me and we cuddled for a few minutes and then i felt that half of the condom was still inside me! The base was completely out and it was still in one piece with no tears. I’m so scared and i bought Plan B and i don’t know if i should take it.. i really don’t want to endure the side effects other people have had if there’s a very low chance I would’ve gotten pregnant anyways.. Advice?