panicked!!!

Hey, so I just had sex about an hour ago... and the condom came off at one point. BUT he didn't finish at all and said that it was fine that he lasts an hour and we barely had sex for 35 minutes ( we took breaks, etc.) He is pretty big and so it's a bit of stretch sometimes if you know what I mean. Now my like inside hurts on the lower part of my tummy, like a cramp but different, and I'm freaking out. Is this a bad thing?! Should I be worried?! Should I tel him to buy me Plan B?! I have no idea what to do someone please help