If steaming doesn't work and the quilt can be washed, wash it, spin out the water, and lay it out on the floor, maybe on top of a plastic checkered table cloth and pin it to the carpet to square it up. Let it dry & if it starts to curl, pin it down some more and let it dry.

If you've got spots that are loosely quilted that are puffing up, you can always go back and add more quilting.

In addition to Margo's comments, how you measure and cut your sashes or borders could be the problem. It's best to cut your long sashing strips parallel to the selvedge (lengthwise grain) because there's the least amount of stretch. If you cut your sashes along the crosswise grain or did not take the time to measure properly, you can easily end up with a quilt that doesn't lay flat.

Thank you for your suggestions. This quilt has no borders so that's not it. I quilted on a domestic machine. Think I will try steaming.

Hi pnunnink and welcome to the forum!
There are lots of reasons that your quilt does not lie flat after quilting it.

First of all, was it flat before you started?? Are you working on a domestic machine or a long arm or did you hand quilt it?

Was it well basted or secured square on a frame?

Is the density of the quilting even all over the quilt? It sounds like you may have more dense quilting on the borders causing the center to be puffy.

Have you blocked the quilt? That may help. Or possibly steaming it? Be careful if you have used markers that would be heat set!

Just finished a quilt, laid it out on the floor and there were ripples in the middle. What causes a quilt not to lie flat? I ditch stitched and then did an all over quilt design. Help!