Plan B or not?

I'm on Orsythia for birth control. I started back in April. I hardly ever missed any pills, even though sometimes I forget to take it at the same time everyday. I had sex earlier today and he came inside of me for the first time. I'm just really nervous that I could possibly become pregnant. I'm not sure whether I should go out and get some Plan B or just wait till after Sunday, since it will be the week I take the placebo pills in the pack and have my period. Any advice or suggestions would be greatly appreciated!