Remember that a circle is 360 degrees, so if you want a 9 degree ruler, you will need to carefully fold your circle into 40 sections (360 / 9 = 40). The sections will need to be folded accurately or your block will not sew together correctly. Again, for these very narrow angles, you might be better off purchasing a specialty ruler.
The folded paper method works great for larger angles, such as 90, 45, 30, 22.5.