Unable to thicken

Hi,

I picked up a vase to 3D print but the model is rubbish.

So I decided to recreate it on SW (I don't know how to use other softs).

Using the STL I put some key points on a 3D sketch that I linked and created surfaces, then I knitted the whole. But now I OMFG cannot thicken it, neither can I shift (?) the surfaces, neither can I create a solid while knitting it.

Help would be appreciated,

thanks in advance !

EDIT : I just thought it's possible to use a surface for a STL and there's no problem to 3D print it...

Though I'm curious to learn why it doesn't work with SW...

SolidworksSurfacing