Used a marking pencil on the WRONG side (green lead...wouldn't you know it? lol! )
Not pictured is me folding the whole thing in half, then in 1/4 and ironing an "X" into the center. Then I placed a safety pin and flipped over.
Attached 2nd safety pin to the first one and created an easy arc with a piece of cotton yarn tied to the marking pencil and safety pin.
Used the short end of the string to make the center...that worked out, didn't it? :lol:
Drew a line from the center safety pin to the edge, cut with scissors then serged everything.