What are the chances?

We had sex without a condom, my <a href="https://play.google.com/store/apps/details?id=com.glow.android">glow app</a> said I was at a 3% risk for pregnancy, and he didn't cum, and there wasn't really any precum. Last time he came was Sunday so he's peed many times since then. How likely is it that I'll get pregnant and should I take Plan B? Neither of us have much money to spare. My period is due on Friday so I think that's a little too long to wait before taking it. Thoughts?