Headway nested blocks?

Hi,

I’m relatively new to using Headway, but have some experience over the years of CSS and HTML.

I’m trying to create a front page that starts with 2 columns (main content and side bar), but under the first content box, it splits into a further 2 columns. For example:

Here are two pics one of the grid and one or the resultant design:

https://chapschoir.files.wordpress.com/2014/11/screen-shot-2014-11-18-at-14-30-23.png

https://chapschoir.files.wordpress.com/2014/11/screen-shot-2014-11-18-at-12-03-49.png

At the moment the 2 columns on the left hand side get shunted to the bottom, and rest on the next ‘row’ under where the side bar finishes.

Do I need to ‘nest’ the blocks somehow?

I’ve been through the headway help pages on blocks, but can’t find any reference to this issue.

Many thanks in advance!