Well, a corn snake is a kind of rat snake. Another name for corn snakes is 'red rat snakes.' There are many other kinds of rat snake, though, and many of them look very similar as babies, even though the adults may look very different.
You said your mom got it at a pet store. It probably is a corn snake -- they are one of the most common pet snake, and THE most common rat snake. Sometimes people in pet stores call things by different (or wrong) names, which is why a lot of the time breeders will use the scientific name, to avoid confusion.
Your little snake was probably bred in captivity, from captive bred parents, since breeding corn snakes is not really that hard. So it doesn't matter if you're from a place where they don't naturally live. People all over the world keep and breed corns (which is really cool, actually, and here on kingsnake.com you can talk to a lot of them!). I have four, myself.
Gizmo (great name) does look like a very cute corn snake. Even if he is one of the other kinds that look sort of the same as cornsnakes when they're babies, it shouldn't make that much difference how you take care of it -- they all need pretty much the same things to be happy and healthy.
So, if you look for information on how to take care of corn snakes, you should be okay, and information on corn snakes is not hard to find! You're in the right place already, and going in the right direction.
Congratulations on your first snake! I'm really excited for you, and I know you'll love caring for Gizmo and watching him grow.
I will look around and add some links for your to look at. Until then, enjoy your new pet!
--Naamah