We'll just have to check the excursion page from time to time and hope they add some more as we get closer to our departure date. I'll post something here if I see any additions. Good luck!
We are on the January 7th sailing on Regal and noticed that too, only 3 excursions available in Belize. But I also noticed on the map image of our itinerary it says Costa Maya (Mahahual, Mexico) may be substituted for Belize? Maybe that has something to do with it?