Just checked tonight to see what was available, and it looks like they either had some cancellations or they opened up another block of rooms! This time I was able to reserve the room with the double beds (which means that I don't have to sleep with either of the kids!). The Holiday Inn reservation system was kind of screwy, though - I was supposed to be able to edit the existing reservation, but the web site puked every time I tried (the dreaded "blank screen", which is arguably worse than an error message). I ended up having to make a new reservation (and making sure it was confirmed), and then cancelling the original reservation.
So, if you didn't get the room you wanted for Duckon, now would be a good time to check again!