Does plan b work?

My fiancé and I had sex last night and he ended up finishing in me. I’m 4 days away from my fertile window but I’ve had discharge like I’ve already ovulated. I thought I read something that says plan b only prevents ovulation and doesn’t work if you already ovulated? Also, I’m around 200# and I believe weight is a factor in the success?

We’re usually very careful and we’ve actually been talking about not preventing but not trying, but our wedding is 7 months away and although we got caught up in having fun and are prepared to accept the consequences, I don’t think I’d want to have a big bump on my wedding day