how to incorporate Amazon astore with theme Twentry thirteen (too thin)

I’ve searched for where to put the style class that I have in the styles.css that only changes the width of the contant of a page content of one particular page. I know to use:

if ( is_page( 5 ) ) : ?>
<?php endif; ?>

I am adding an amazon associates store to a page. my theme is Twenty Thirteen and the content for the page content is about 150 px too narrow for the store to display. Nothing I can change on amazon settings so I am trying to code out the problem for that ONE page.

The amazon astore is an <iframe>. I tried embedding it, same problem

I’ve created a child theme and have it activated.

As I mentioned, I selectively deleted the sidebar for the amazon page and the content area does not change – only shows part of my astore.

Any ideas?