HELP: Pregnancy scare?

My boyfriend and I were having sex on Saturday (March 4. It's now the 9th), and the condom broke. We realized about a minute or so after it broke. He said he realized when he pulled out and saw the head of his penis. He didn't finish and we changed condoms immediately after that. My period is only late by 1 day so far, and I've been under a lot of stress for the last month or so (I'm stage managing a musical with 10+ little kids, which is a story for another day), but I'm still kind of freaking out. I know stress can cause my period to be later than eve. says it should be, but should I be worried or is it all in my head?