What do you say when you want to do a follow up for a job?

I had my 2nd interview on Tuesday (July 26) at Ross. It went pretty well, towards the end of the interview the guy offered me a position and asked if I was willing to go through a background check I said sure. He informed me that background checks would take normally around 2-3 days and 1 day if the person has no past work experience. Well since I don't have any work experience with paying jobs just volunteer work I figured okay my background check should be quick. I know my record is clean I've never gotten in trouble with the law and I don't do any drugs or drink. Yesterday I checked my email and noticed I got something from the company that does the background checks saying I needed additional information to proceed the background checking so I called and some lady answered and she said my background has been checked yesterday (Wednesday July 27) that now I needed to check in with Ross. It's Friday now and I'm a little scared I wont be getting a call back. Should I be the one to call back and do a follow up? If so what do I say?