they hold back some Palo reservations for people to book on board so you may still get in. Our first time on the Magic we couldn't get anything online, and when we got on board those had filled up also, but we put our name on the waiting list and they called our room a few days into the trip to let us know they had an opening for us.
If you don't get in at all it won't make or break the trip, but if you can get to the brunch.... it's yummmy!