Can you show us some pictures?
I have just done the same and took out a small part of the stitching,,, about 6 inches either side of the problem area..
Then put it back on the machine and re sewed it, paying attention to letting the machine do the work properly..
Are you using a walking foot? if so, just let the machine do the work and it will ease the pucker away...make sure you have the quilt flat and smooth when you start...
Hope this helps and you have success...