Yes, you made a mistake buying this timeshare, but I know a lot of people who own Marriott timeshares, my son's in-laws included, who don't have any second thoughts about their developer purchases. These owners love the Marriott Points for the flexibility, and they would never buy a resale because it's not as flexible (no Marriott Points).
You bought it, and even if you think timesharing is a gamble, a lot of us here do not think it's a gamble at all. Sure, if you expected to trade into back-to-back weeks in 2 bedrooms at the Marriotts on the islands during whale season, you might be disappointed, but you have a better chance than I have to do just that. I don't own a Marriott, and the Marriott preference is very desirable.
We don't know your financial issues here, you haven't divulged that much info, nor should you, but if you can afford it, just keep the thing and pay it as you once enthusiastically decided. Signing on the dotted line for a timeshare has its consequences. Walking away from that loan will haunt you for many years. And the resale value of your week is so disappointingly low, you will never recover enough to pay that thing off. If I remember your first post correctly, you still owe around $15K. The week may be worth only $3K or less.