So, the drawstring bag became a change mat. Some ripping of seams took place to move some strips, slightly wider borders were added and a backing fabric chosen (DD and SIL love ducks). The stripped top was sewn to the flannelette backing just as one would sew a drawstring bag (with only four inches left open at the top for turning it in the right way) and voila! One change mat.
Now it just needs to be quilted (so it doesn't become misshapen in the wash) and it will be done. The quilting marks seen above have been removed - it will now be quilted diagonally between the rows of ducks on the flannelette backing.
What a lovely Easter project. DD is quite proud of herself!