did you baste from the center to the edges?
did the top lay flat before you started layering it with te backing and batting?
can/will you post pictures of the whole quilt? if we see more of it, we might get a better idea of what is happening.
when i have layered quilts, i have noticed some creeping. so - i have learned to start from the center to the edges or to start at one side and keep on going to the other side.
when starting at opppsite ends, i usually ended up with a pleat or bulge in the middle.
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