HELP when to start birth control?

okay, i got birth control i haven’t started it yet. i just got my period today, june 7. i was going to start it the 10th of june as the doctor told me to so i wouldn’t be on my period on july 20-22, since i have plans. i don’t want to be on my period on july 20-22, so when would it be appropriate to start my birth control? would starting it the 10th of june make sure that i don’t get it the 20-22 of july? help!!!