pregnancy scare

Can someone please give me advice, me and my boyfriend had unprotected sex yesterday and I thought he had on a condom but he says he did not cum in me and it was in his hands I saw it but maybe I'm just paranoid but I feel like some of it still got in me, but I really don't know if I should buy a plan b cause if I'm not pregnant they could mess me up right ? I just don't know what to do I'm really scared and I can't get pregnant