I would take off the last row, then measure to see whether it's actually shorter than the others. Chances are it's very close to the same size, so you would just need to ease it in. Pin at both ends and in the middle first, then all along the sewing path so that the edges match. If it's really that much different in length, compare to the other rows to see where the problem is and fix it. It's a very pretty quilt, and you can fix this.