LFS said it was a catshark huh?
Banded bamboo shark. For some reason stores call these things catsharks when they are not true catsharks. Pet peeve of mine. Anyway, it will get to be between 15 and 18 inches when it is a year old. After about 6 months you'll notice the dark black and bright white bands will change to dark brown with tan stripes. Going 3 days is not a lot. Feed it daily and look out. You'll have a monster on your hands before you know it. Did you hatch this one or get the pup? Are you planning on putting this in your tank at work? You must have a lot of space. These things get about 40 inches as adults and you're going to need a 300 gallon tank eventually.