Shut off surface not showing up

Hello.

Im trying to shut off surface on my model, but preview and applying the feature doesnt show it.

First time using molding tools, so i have no idea what might be the problem.

Is it the fillet ? Ive tried without the fillet but the surface was like a big balloon.

Is it necessary to have those fillets at the bottom ?

SolidworksPlastics And Mold Design