Yeah, those aquarium kits are always a rip-off, which is why I put together a list of things to get yourself.
In the incandescent is a problem as it can heat your tank up a lot. I wouldn't be surprised to see your water at 95 degrees on a warm day! Luckily you can take the bulb out and screw in a compact florescent (the curly kind). It'll be much cooler for your fish.
Also, you're still gonna need a heater...
Just fyi- walmart has an insanely good return policy, so you should be able to return the tank still if you want to.