1 piece of 1/4" or 2 pieces of 1/8" to prevent spr

I read the Benroy plans above and it recommended covering the galley hatch with 1 sheet of 1/8" to prevent spring back - however, I've already done my whole roof in 1/4"..so to keep everything flat I need to go w/ 1/4" on the galley lid. The curve is pretty gentle and I can bend the 1/4" no problem, but would it be better to have 2 pieces of 1/8". Which would be best to prevent springback? Total of 5 spars. 3 are 2.25" wide (2 pieces of 3/4" plywood and 1 piece of 3/4" poplar glued together) and 2 are 1.5" wide (2 pieces of 3/4" plywood glued together), all are 2" deep.
Spar curve template:
Spars and blocking in place till glue dries.

Spar curve template:
Spars and blocking in place till glue dries.