One thing that I haven't seen mentioned yet is to steam the area that you are quilting. Use your iron to try to shrink the fabric slightly and eliminate any fullness that may be developing in the top layer. I'm doing this now on a quilt that I'm working on that has one block that's a little bigger than it should be and doesn't want to lay completely flat. Ironing it with lots of water and steam seems to be helping. Besides shrinking the block slightly, it is also reactivating the basting spray and helping it adhere better. Good luck
~ C