What you are trying to achieve is not possible using a page template with sidebar. By default main content container and sidebar are side by side.
To achieve that instead, please use either fullwidth, or with container page template. Then build the structure inside Cornerstone builder. On first section, add column only to make it fullwidth. Then the next section, use like 2/3 and 1/3 columns. On the 1/3 column, build the content of your sidebar.
Below the navigation, BELOW MASTHEAD option is available per page. This is another way of showing a fullwidth content below navigation or above your content. If you can build your content using REVOLUTION SLIDER, that might be possible with current page template.
Hope this helps.