Do plan b works if your period is 9 days late?

So I have irregular periods all the time and recently me and my bf had sex and the condom slipped, so we got a plan b and I took it. Is there any possible way I still can get pregnant after taking the plan b and my period already being late? (And yes I took a pregnancy test the day after my period was supposed to come on and it was negative) I’m just scared and I need some reassurance.