Plan b. Help!?

Whitney
Gonna try and keep this simple. 
Umm.. So my period is a bit late. I was think it's because I had sex on the day it would've started, and I haven't had sex in a while. 10 days late, I THINK. So I had sex again last night, the condom broke. I freaked out took plan b, about an hour afterwards.  Then I read somewhere that it doesn't work well with women over a certain weight. I am above that weight limit.
Basically I just need to know if it's going to work or if I just took it for not reason.