That is called a valance and you need to make a pattern out of hardboard, metal or pvc. Layout your material and trace pattern on with water soluble pen or stabilo. Cut out pattern on material with scissors. Then to finish it off a cotton strip that gets sewed on around the edge.
Better to take to an awning company that have right sewing machine and let them finish it off for you.
If it is red vinyl material you can paint white strip with vinyl screen ink from NazDar thinned with their reducer.