Plan B one-step

So I had sex last Sunday and the condom tore(completely tore), and I wasn't on my regular birth control pills at the time. Everything obviously got in me as we didn't realize the condom was torn until afterwards. I took plan B one-step within two hours of having sex, and am having some major abdominal pain on and off. I'm still worried I might turn up pregnant. Can anybody give me any advice on what to look out for?