Pinch a fold of cloth at the dashed line, and fold to about halfway to the next dashed line (represented in the image by the dotted line)
Repeat this 2 more times
Flip the project around again.
Fold the lateral edges at the dashed line, and then fold again to make the hem.
Use twill tape 3/8 inch wide, Cut 4 strands of twill tape, approx 35-40 cm
If you don't have twill tape you could probably use any string-like thing (ribbon, shoelace, bias tape, paracord). However it would be best to use cotton material for ease of washing and sterilization. (Nylon or other plastic material may melt in a heat-sterilization method.) Cotton also tends to slip less than nylon/polyblend.