The picture you have shown is what I call a french edge and some would call a french rolled edge. It is easier if you don't make your corners too sharp and don't pull the corners to tight as you pull the strip around them. I usually work out my width of strip needed, skive 1/2" back about and start face to face and free hand stitch it around on the sewing machine with the 2 edges level. Finish stitching an inch or 2 short, cut off to match the skive and skive the top piece.Glue together and fini