Is Pregnancy Possible While On Microgestin Borth Control Pills?

I started taking Microgestin exactly a month ago. This is my first time ever being on any sort of birth control. This last week was my week of placebos and my boyfriend and I had unprotected sex last night. Should I take plan B? Or should it be alright? I am 19 and he is 22. Neither of us is ready to be a parent...