Drywall Arch

I have a doorway arch that I need to drywall. The width is 34.5 and drop is 10" I calculated that to be about a 20" radius. Is this too small to use 1/4 drywall? I have tried wetting/scoring the front and back, doesn't work. I am now setting the strips in between 2 sawhorses and wetting them every hour or so to get a natural bend in it. I also have the cutout of the arch, so I turned it upside down and used it as a form and placed another wet strip over that. Is there something I'm missing? Is the radius too tight? Any suggestions?