Stressed...

So my boyfriend and I had sex on June 7th (Saturday) and we're pretty sure that some cum got inside of me. I took Plan B that night (like 2 hours after sex). The next day (Sunday) I started up my birth control pills. Is there a possibility that I could be pregnant or no? I'm not sure if taking birth control the day after the Plan B could've made the Plan B not work... I've been stressing for awhile about this. Please respond to this!