It did seem a little weird, considering he had just blatantly used the power of “please” to command her to sit. But I think these deals can be interpreted hyper-technically, and it is always possible Regina could have dropped it on the floor and then handed him the pieces — a risk Gold wasn’t willing to take.
I also think it suited his agenda to get things out in the open with Regina. Things are clearly starting to happen so he may figure that the time for shadow boxing with Regina is over and it is time to take the war to the next level. I could be wrong but what I DON’T buy is that he just forgot, or was too overwrought with emotion to wield his power.