the process of quilting (just like the process of applique and embroidery) always draws up the fabric some---dependant upon the amount of stitching done...it is a normal occurance and the reason for having extra fabric (when embroidering/appliqueing you cut your squares 1" + before doing the work-then trim to size when completed- with quilting the backing/batting is cut larger- then everything trimmed/squared after quilting)
if your center is skewed---perhaps you did not (stablize) it before quilting? generally the edges (inside the borders) should be stablized-then quilted (from the center out) then the borders quilted- then the whole thing trimmed/squared-
if you show us pictures we may have an idea of how to (fix/square up) your project- or if you did not quilt too densely you may want to remove the quilting, stablize & try again...if it is densely quilted there may be a way to block it...we need to see what happened to have ideas on (help)