Thom, good start sir, keep us posted. Others here can give advice more expertly than I.
I think a majority of folks use one clay to 3 sand, then mix in straw ....was your grass dry in your mixing?
One trick I learned in Cub Scouts camping, to avoid a thrashing at home, was to smear dishwashing soap on the pot before the open fire....an easy cleanup before sneaking it back into mother's cabinet.