Mark only on the bottom about 1-2 inch mark. This is where you will not sew. It is used to turn this right-side out. You will sew all the way across the top and then Sew to the blue line on the bottom, skip that middle section, sew from blue line to the end.
Don’t forget to stop at the blue line and not sew that area. Otherwise you will have to use a seam ripper and cut those stitches out. Yes! I actually have done that. Plus, if you do sew it all the way across, there is no way to turn it about.