Making page full-width does not render page as full-width

Issue Summary

When rendering a page as full-width in the new editor, there's a large amount of whitespace on both the left and the right side. 

Users want to be able to use full-width so their pages utilize as much horizontal space as the page allows. 

Steps to Reproduce

1. Create a page in the new Confluence editor.
2. Switch to Make page full-width. 
3. Make sure your browser window is maximized to the full page so you can see the amount of whitespace that is left behind.

Expected Results

The page should stretch from one side of the editor window to the other.

Actual Results

In this case, there's a large amount of unused space.

Workaround

No current workaround.