Yes, this has happened to a lot of people and you might have read about their stories on other threads here. When you were booking the dining, did you look at the billing page at all? Did you see the total to be charged (say, $78 for two)? Did you see any credit applied, bringing the net owing to $0? Or, did you see the amount owing was the same $78? If you saw that, why did you go ahead if not wanting to pay? Try booking another SD reservation and examine the billing page and see if any credits are applied. You can back out and not confirm the second res if not wanting it. If you don't want to pay, just cancel the res you made and your CC will be refunded.
There are a lot of issues with the App and DMW. You can either wait until on board, or you can try the booking using the Web version of the App. DMW is part of the Web version and several have reported better success there.