your batting needs to be (at least-more is better) 4" all the way around larger than your top- while stitching it (draws up like embroidery or applique) so you need more to make up for that- after the quilt is quilted you trim your backing-batting to fit the top---but they should start out larger. and measure twice before loading- to make sure you have the length going lengthwise and the width side to side.
i have so many times pulled the batting out- looked at it and (thought) i had the long part in the right direction only to find it was sideways---always measure to be sure.
but if you add that extra (8" in both direction---4" per side) you will come out ok.