Question about Plan B..

Condom broke when I was in my fertile week according to the app. This was 3 days away from when the app says I was supposed to ovulate. Well I took plan B just in case it worked. I'm now 3 days away from my period and I'm so very nervous. I want to test tomorrow, would that be dumb? Also I hear that plan b can delay your period but at what point would I believe a negative test IF my period doesn't start?