Is it one of those gift card giveaways from their Total Reward program or for staying in their hotel (or one of the many Harrahs owned hotels)?
If so, they usually put final sale on the receipt so you may not be able to exchange it later. I am not sure if that is still the case today though, things may have changed.
Just buy your girl a bag or buy yourself a new luggage, or a toss a loafer or two my way, maybe a pair of boots. I'm a 7.5G.
One thing that might work though, is pretend all your purchases will be a gift and ask for a gift certificate and maybe you can do an exchange that way.