Your binding should have the quilt sandwich in it so that it doesn't lay flat. I off set my binding 1/4 inch and leave a 1/4 inch of batt and backing extending so that when the binding is rolled, the entire binding is filled with batt and backing.
And don't just stitch from one end to the other. Measure the center, both width and length, to get the proper edge measurements for binding. For example, if the center length measures 95", but your border edge is 97", cut the binding 95 + extra for turning the corners. Mark the half way points of both the binding strip and quilt, then the mark quarter points of both. Pin the binding to the quilt edge, matching the markings. Fit the quilt's longer edge to the shorter binding and pin in place. When stitching have the binding on top. The extra length of the quilt's edge will be worked in and the edge of the quilt will not be wavy, but square after the binding is rolled to the other side and stitched in place.
SandyQuilter