Slideshows are meant to be used filling the total available space or at a minimum displayed as a "block" with no content to the left or right - so you'll need to apply css specifically to that page. You can do that using the following classes:

- Add the <?php body_class(); ?> if its not there already

- Inspect your about page and the classes in the body - you'll have a class with the ID, a class if there's a special template in use or possibly a class with the page slug then use it to target just the nextgen gallery inside that page.