If it is the vertical edge which needs closing I would make an edge which is turned over twice, so the raw edge is enclosed and held firmly.

Depending on the thickness of the fabric the edge should be about 3/4 of an inch, with about 1/2 an inch hidden inside.

The type of stitch is not all that important unless it is going to be inspected. A running stitch done from the wrong side so that only small stitches appear on the right side is fine, as long as it is not so tight that the sewing thread might snap under tension. Whip stitch works too, where the thread spirals through a few threads on the inside of the outer layer, then through the folded edge, which can be almost invisible but the edge can become more tubular than flat.

Anne the Pleater :ootd: