The Pill and Plan B question

So a couple of weeks ago (about 3), my boyfriend and I had sex for the first time. I had not had sex before this in nearly a year. I have been on the pill for about 4 months now due to acne and period regulation and I do take my birth control regularly every day. I’ve only have had to take 2 days worth of pills one time back in September before having sex with my boyfriend. Here’s the issue: During sex, the condom fell off. To be safe since I’m relatively new to taking the pill, I took Plan B about an hour and a half after sex. Regardless of all of the precautions we took, I am currently 4 days late on my cycle. I don’t know what to necessarily do. I am super anxious about this as I am a freshman in college. Please help.