Directions for use:
1. Position the edges of fabric in center of fold-over elastic.
2. Fold elastic over raw edges and pin at beginning.
3. For smooth edges: Set the stitch to a straight stitch or a narrow, medium-length zig-zag. Carefully guide fabric and fold-over elastic under machine needle and stitch.
4. For gathered edge: Guide fabric and fold-over elastic with one hand as you stretch fold-over elastic tightly with other hand. Then straight or zig-zag stitch on edge of fold-over elastic, catching all layers.

** Sometimes elastic will ease out a bit after being stretched, kind of like how some fabrics shrink after washing.
So, it’s a good idea to give your length of elastic a few stretches before you cut.
A pre-stretch, just like you pre-wash your fabrics.