Surface corner is not smooth enough.

Hi,

I am trying to make a back cover for an e reader (LINK) using surfaces.

However when I make the surface using either Lofted surface or Boundary surface I end up with a weird shapes in the corners of the backplate.

How can I get rid of these?

Creating another guide sketch 2/3 up from the ground surface  doesnt work either.

Any ideas on how to make this smooth?

Thanks,

SolidworksSurfacing