As always the fine print of "Dealer participation may vary" seems to never be truer than in your instance.
If the the dealer wants the car back, take it back. I'm a firm believer that things happen for a reason. He may find another cheaper.
Plus X-Plan caps the "Administrative Fee" I believe to a maximum of $250 or lower. Most dealers charge $395 to $695 for this "Fee" at least in metro Atlanta.
No need to get upset now. Just make sure you have your PIN when you get there tomorrow.
You know what was discussed and obviously so...