Plan B?!

So me nd my bf had protected sex yesterday but the condom ripped like it ligitamit ripped but he always pulls out before he cums even with a condom on . So I felt when his cum fell on my butt , but he wants me to take a plan B pill just in case . But where planning on having unprotected sex for the first time maybe today or tomorrow we don't know yet . My question is will the plan b pill work for both days or will I have to take two pills ?!