Plan B?

Okay I’ve been using this app for almost a year and it’s gotten to the point where my periods are exact with what the app says. I got off my period about a week to a week and a half ago. And so less then a week ago I took a Plan B pill as a cautionary (which I’ve never done). And this morning I woke up and there was a little blood, but I’m not scheduled a period for over two weeks. I’m freaking out, should I be scared?