Really bumpy

[u/Rollamon]

So ive put foam clay ontop of cardboard to combat the warping (as seen in red) but the cardboard isnt layered. Now in the second picture ive put foam clay ontop of normal heatsealed eva foam (as seen in green). My issue is that once I applied some mod podge onto the green its really emphasised the bumps and im not sure if it will do that to everything circled in purple. I have sanded down everything inside purple but alot of it cant be sanded down further due to it only being a thin layer of foam clay. Is there any way to fix everything in purple so it doesnt turn out like in green?