I would take the border off and "block" the top. Sharon Schamber has videos on Youtube for doing this. Basically she spray starches the fabric and then steams it to shrink it into shape. When you add the borders, be sure to measure through the middle of the quilt first and cut the border to that measurement; pin centers and edges first, then pin in-between, before sewing on the border. Sew with the border on top so the feed dogs can help "shrink" the edge to the border.