plan b

So I just had sex with my boyfriend and we used a condom but he pulled out and then like came on my stomach like he took it off for some reason and then he was worried some got in so he looked down there and he said he saw white on my like sorry for detail but lips and then he said he didn't know if it was from him or me and he wants me to get plan b what should I do? I don't have a lot of money for plan b Please give me advice