My boyfriend underestimated himself

So lately we’ve been having more and more sex and we’ve used condoms in the past but it’s the most stable relationship I’ve had so I said screw it about a month ago and we stopped using them and his pull out game was always great up until yesterday he underestimated how much time he had. I’m on a low dosage birth control so I was freaking out knowing that wouldn’t do me any good so we got a plan b and to be honest I don’t know what to expect I don’t know how to know if it worked or anything. We both want to finish college before even talking about having a baby. I’ve never had to buy one before so I’m not sure if I should also buy a pregnancy test to be safe. What do y’all think??