To more directly answer your question, you can't have someone just step in at this point. The ROFR process would have to start over. So, you might be able to find someone else to buy the contract, but you'd probably have to provide some incentive, or have a really desirable contract. I couldn't find you in the ROFR thread, but I did find a post where you said you're paying a lot, so I would think you'd have a difficult time finding someone else.
If you back out now, you'll lose your $500 deposit. If you go through with the purchase and then turn around and sell, you'll be out the closing costs plus the brokers commission. That would normally be much more than $500, but for a 25 point contract, it might be close.
If you're happy with the resort and use year, I'd just look for a second contract to "add on" with this one. That way, you're only out the additional closing costs, plus whatever premium you paid for the small contract. I guess if you paid $20/point more for the small contract (times 25 points equals $500), then you'd be better off cancelling the deal and losing your deposit.