Step 5:
draw the continous line between the 0% and 10% mark along the selection.
Fill the area between 90% and 100% with a pure red color. Dont care about the arc on the outer side of the area, that will be done next. Shrink the selection by 10 pixel and disable the shrink from border checkbox. Invert the selection and draw the outside of the red area.
Remove the selection.