Element offset with the 2d and 3d elements

Hi

I am currently modeling a chair and I would like to create a solid element core material between the two shell elements.

First, I perform element offset with 2d elements and duplicate them so that I get a similar 2d shell elements at a particular offset.

Now I try to perform element offset with the solid layers option and try to offset the shell elements at the same distance value with that of the previous offset but the solid nodes and shell nodes are not getting equivalenced. There are some gaps between the nodes. 

Is there a better way to create a core between two shell elements for a complex geometry on different faces than to create element offset?

Thank you.