You may want to check the receipt and see how much you paid for the PS3. You might not be getting back as much as you think.
Most of the times when they do this rebate promotion, they deduct the cost of the rebate from the item. As this was a $100 GC, you paid $299 for the rebate. Or, they may not allow you the return of the PS3 without the GC, and they'll deduct whatever use of the GC you did from the return price.
As I'm guessing you're trying to stiff someone out of another GC, I'd recommend not doing it.