The purpose of the fob slot is to allow the car to be started if the Intelligent Key goes dead. Placing the entire fob (not just the metal key) activates the override function which allows the car to be started with a dead battery in the fob.
I suppose it's not necessary to point out that the metal key is ONLY used to open the doors or lock the glovebox. The fob slot is not a key slot. The owner's manual is quite clear on that point.
The thing to be concerned about is that you may have broken the override function. That is, you''d better check to see if you can start the car by placing a dead fob in the slot and holding it there as you press the Start button. If not, then I suggest you ask the dealer for an estimate to fix the damage done by this mistake (that is, if you ever would be stuck with a dead fob again then you might want the override function to be working correctly). I hope that answers your question simply and clearly.
Oh, and you can buy the CR-2032 batteries almost everywhere. Target, for example, sells them for about $2 for two batteries in a single pack. No need to shop eBay or pay shipping charges. This is probably the most common "coin-type" battery made.
Good luck.