Hi, Nancy!
Do not give up hope! Let's try a few ways to get you a reservation for T-REX in Downtown Disney!
-Try checking the first thing in the morning
HERE to see if you can snag a reservation. Sometimes I have good luck early in the morning, after the computer system has reset overnight and hopefully there were some cancellations the prior day that can now be yours!
-Give a call directly to the restaurant at (407)828-8739. I would not recommend this for most restaurants at Walt Disney World, but for T-REX, give it a try. Try to call before the lunch rush so they will have time to work with you on a date and time.
-If you still are not having any luck securing a table, you can always try doing a "walk-up" when you get there. Go during "off" meal times - avoid noon or 5:00. A late lunch or early dinner might be your best shot.
Good luck to you! I really hope you get the chance to dine with some Pre-Historic friends!