I guess we'll start planning our first trip! Thanks for your help.
If the three days (midnight, third day) has not happened, don't give up.
TIME IS OF THE ESSENCE!!!
Send them a WRITTEN cancellation, either by FAX (with proof of receipt) or by certified mail (get a 'proof of mailing' from the USPS).....
The Texas laws about the right to cancel a consumer contract (PDF) can be found online at:
http://www.statutes.legis.state.tx.us/Docs/BC/pdf/BC.601.pdf
However, based on your later post, it also appears that this transaction would LIKELY fall under the Texas Timeshare Act, which gives you even more time to cancel... and restrictions on the seller.
You need to read the information (specifically Subchapter E) in the following PDF document:
http://www.statutes.legis.state.tx.us/Docs/PR/pdf/PR.221.pdf
Without further facts regarding the transaction.... and where it was made, etc., no one can close this door for you. TIME IS OF THE ESSENCE and if you don't at least follow the rules to cancel (even if you don't have the legal right to do so), you will absolutely LOSE them.
DO IT NOW!!! Then, AFTER you have sent them the notice, take the time to research as to whether you had the right or not. Their including a 'no rescission' clause means nothing. You cannot waive your statutory right.