Don’t want to get pregnant yet!!

So i stopped taking my BC at the end of feb to possibly get pregnant but I changed my mind and I’m not ready... my projected ovulation day is tomorrow. I have been having sex this whole week unprotected with my Significant other... i went to get my prescription of BC today... is it going to be effective if I start it today?? Will it prevent the pregnancy?!? Veryyyyy nervous! 😫