How to get a surface of uniform thickness?

Hello,

I have created a bone plate using the loft feature. However, I am unable to thicken the surface using the 'thicken' feature as this is showing an error.

I have hence used the surface->extrude feature but this has resulted in only the boundary of the plate to me raised by the required amount (0.1cm).

If I try to use the surface -> fill feature it does notuniformily thicken the entire plate.

Any help would be appreciated. I have attached the file below.

Thanks.

SolidworksSurfacing