For Christmas last year I made each of my teenagers 2 pillowcases using this 'hot dog' method. I made the contrasting piece a little bigger than needed and every time it gets washed it starts waving at you and needs to be ironed.
Never again. I took it to the sewing room and top stitched the edge down. I took a few pictures so you can see my method of getting the edge top stitched down perfectly with NO TROUBLE. I use this blind hem foot for my machine.
Position the foot with the edge of the black fabric against the blade of the foot (mine is black). Move the needle over so that it stitches to the right of the blade.
Here you can just barely see the stitches that I started with, (without my blind hem stitch foot) and without changing the bobbin to a dark thread....those stitches came out. The blade rides along the ridge of fabric and you get perfect top stitching.
It is hard to see the stitches here so I did a sample with white fabric too.
Perfect! Here's the new and improved pillowcase:
Can you guess whose pillowcase this is?