Dang! Now you got me curious. It's tympanum looks too small to be a juvenile River Frog or Bullfrog. Also, the River Frog has a fairly dark underside with some light markings. From what I can see in the photos, it's underside appears fairly light colored.

What about a Dusky Gopher Frog (R. areolata aesopus)? Mature specimens are around 3 inches and since it was held at the pet shop for some time, it probably isn't a juvenile.