Scared

So I recently had sex with a guy this past weekend (who is clean, and I've been seeing for a while) and I'm pretty worried that I might be pregnant. We used a condom in the first round, he finished, everything was fine. Then in the heat of the moment we started back up again without a condom, and before it got too intense we stopped and I made him put one on. I'm just worried that the precum + leftover ejaculate could cause me to become pregnant. I want to use Plan B but I'm worried about using it again since I used it earlier in this cycle and it has caused me really bad cystic acne.... I'm not looking for lectures about being promiscuous and I already booked an appointment to get on regular birth control pills with my gyno. I just need reassurance/advice if taking Plan B twice in a cycle is safe.... thank you.