You would need to cancel (the legal term is rescind) the purchase.
My advice in any timeshare purchase, from any developer, is if you have even the slightest doubt about your decision, rescind and start over from scratch. That is exactly the reason there are rescission periods to begin with.
Take your time, and study the question carefully.
The first thing I urge every potential buyer to consider is whether they really want to enter into a 30-50 year financial commitment to a timeshare -- or in the case of most other timeshares, a never-ending commitment. In order to answer that question, you have to look far into the future and try to guess how your vacationing needs might change as you have kids, the kids grow up, you retire, etc, etc.
You also need to realize that DVC covers only lodging, and the other costs (park tickets, airfare, food, etc) are not covered and many of those costs have exploded in recent years. So even if you lock in your lodging cost, Disney vacations are still going to be an expensive vacation option and may increase in cost faster than other options.
In the case of DVC, I would look at two additional things -- your past history of WDW visits, and the capabilities of DVC beyond WDW. People sometimes purchase DVC after their first-ever visit to WDW, or their first-ever visit with their kids (like me, for instance!). If you have a history of numerous visits over a period of years, I think you have a much sounder rationale for purchase than someone dazzled by pixie dust.
I think any prospective DVC purchaser should also really consider how they might use this timeshare for non-Disney vacations. The fact is that DVC is a very small system, heavily concentrated at WDW (9 out of the 13 total resorts) -- so it is seriously limited once you branch out in your vacation choices. Yes, you can currently exchange through RCI, but those exchanges will often be downgrades from DVC and that capability could go away entirely -- it is a contractual arrangement between DVC and RCI, not something that is guaranteed to you.
If you decide DVC is for you, I would encourage you to take a long, hard look at resale. You may be able to save 30-50% purchasing resale.
If you decide you want to own a timeshare, but DVC won't meet your needs, you should know that there are several other very fine timeshare systems available -- and some of those can literally be purchased for $1 on eBay.
If you decide timesharing is not for you, there are many other options out there to save money on vacations -- particularly at WDW.