I'm thinking that you're going to be fine. You don't say exactly, but it appears that you know that you are within the legal rescission time period (10 days from when you signed the contract) I also assume you sent it to the Ocoee, Florida address- not the resort. It is not important that you send the tablet and other promotional materials by any expensive method, only that you save the receipt that you mailed it in case they try to bill you for something you don't want.
Now that you've sent the rescission letter, it can take up to 45 days to credit your credit card if that's how you paid the down payment, AND they are not required to inform you of the progress of the rescission. Prepare to sweat a little. One way you'll know they got the letter and are working on it will be if the sales department calls and promises you more points, extra vacations, lower price, anything to get you to change your mind. Just don't answer any unknown phone numbers until after the 10 days has passed.
Congratulations for finding us and ducking out of Wastegate. Take a deep breath now.
Jim