Birth control question

Yesterday i wenr to the doctor for a cough i had and my mom and the doctor got to talking and they asked if i wanted the shot so i said why not and boom, like this happened within 5 minutes! Today i really excited so i had unprotected sex and was a little worried after so i googled how long is it until the shot is effective and it said 7 days. Can i get pregnant? If i take a plan b pill with it mess something up??