Keep trying! It’s a great experience.
IDK about walk-ins. You can’t just walk into the restaurant and ask. To go to the California Grill with an ADR, you have to go to a reception area on the second floor of the Contemporary Tower and be escorted up by someone with an elevator key.
I guess the receptionist can check if they have room for your party, but I wouldn’t count on it. You have plenty of time between now and January. Keeping looking and sign up for the Touring Plans ADR finder. Good luck!