Trying to add some responsive code to a free form landing page is very unlikely to work. Either you use free-form LP templates and you stick to what the can do (absolute positioning and a mobile version of the page) or you move to guided landing page templates and you will have full latitude for responsive design, although some features are still missing, including the capacity to add an HTML block (see Guided LP enhancements )
The reason marketo is not closing the divs as you expect it to be, is because marketo's free form landing page template development is not made to create responsive bootstrap enabled landing pages. As a result of this, the elements that you drag and drop in the draft of the landing page are positioned absolute, and there is a method( or you can say a hack) called 'double div' method. Here's the link to it: Marketo Responsive Method: Marketo DoubleDiv | Edward Unthank | YeslerEdward Unthank
This method disables the absolute positioning of those dragable elements, and your content is positioned as you want it to be.
Recently marketo had released another way of developing responsive landing page templates without much hassle. Its called the 'Guided Form'. Here's the documentation of it: Guided Mode (Easy) - Marketo Docs - Product Docs Try switching to this editor because in this editor you do not need any hacks or way-around. Your bootstrap coding will work perfectly in it.
Also, regarding with the container not streching to 100%, could you please specify the parent container's stylings in the code of the template?
I hope this solves your problem.