This has happened to me too (panel going very wonky after pre-washing), but I was cutting mine into strips to fracture so once I got it back into shape I didn't have to worry that it would "revert" again.
I think a lot depends on the size of the panel in relationship to the size of the borders that you put around it. The smaller the panel, and the larger the borders I think will help. And you should be sure to cut the borders on LOG if possible (at least the longer ends of the border.
The type of batting and backing will make a difference as well. A pieced backing, a minky backing, a flannel backing or anything else with more "give" will not help to hold the shape of the panel together as much as a solid piece of good solid on-grain fabric.
And of course the type of quilting will make a difference as well. Heavier quilting in a free-form motion (circles, swirls, feathers etc) will help hold more than straight line quilting (especially ie diagonal cross hatching).
Now ... if you still don't want to risk it ... you can inquire with your LQS about exchanging the fabric, but I wouldn't hold my breath. If you are successful, forego pre-washing on all of the fabric intended for this quilt.
Good luck!!