I want to create a solid from my curved surface.

Take a look at the picture above: I have an original curved surface, and then I made an offsetted one to the inner direction. This offesetted surface should be bounday untill which I want to create a solid.

So how can I do this?

Here is my .3dm file:

http://www.gamefront.com/files/20378138/solid.3dm

 

Thank you.