Paranoid after sex

I am 6.5 weeks PP. My husband and I had sex last night for the first time after my c-section. The soonest available appointment to get my IUD placed isn’t until June 11; so we decided to use condoms until then. I realized when we were done that he had taken the condom off at some point! I was livid. He did use the withdrawal method, but I’m still really upset. I am so paranoid that I’ll get pregnant again so soon. I know pregnancy is incredibly unlikely considering I haven’t had my period yet, I’m exclusively breastfeeding, and he did withdraw after he condom was taken off. Should I get Plan B just to be safe? Or do you think I’m totally fine and should quit stressing? I’m so anxious about it.