Hi
You didn't mention whether you had the trip booked through Disney, or through a
travel agent.
If Disney, I would contact them and see if you can get the deal on your existing reservation.
If through a travel agent, I would contact the agent directly.
We booked our trip for Feb a few months ago, when the deal came out, I contacted my
AAA agent and she was able to get us the discount. We're saving @ $500 PLUS getting the $200 gift card (I believe the gift card give-a-way is only good for trips through the end of March).
Even though the ad is a 4 nite, get 3 free, our trip was booked for 9 days. We get 6 nites, and then 3 free. We still have the Magic Your Way package for all 10 days of the stay, plus the dining plan.
Get on the phone and call and find out!