Oh man.. these fish are very difficult to keep depending on the size and age of your tank. If you don’t have an established pod population, with a big enough tank to support their large appetites, they won’t thrive and will slowly starve to death

. You can purchase pods from algae barn or another source. But I would definitely reconsider where you buy fish if your fish store told you that is a blenny. If you love the Lil guy, you might consider rehoming him to someone with more experience in the hobby. But I definitely wouldn’t take it back to that LFS!
What size tank do you have it in and how old is it?