Hi there, looking at the cart 66 documentation there is the option to add as either a widget, or via an action hook. If you’re just looking to add to the menucard page I’d advise using the action hook provided on their support pages – http://docs.cart66.com/knowledgebase/hooks/

Or place a link to the shopping cart in the navigation menu, like here – http://screencast.com/t/9wT1d26W

Or you could edit the menucard.php to stop it being a fullwidth page, and make it a show a sidebar, then the widget would display. The theme customizer team can assist here if you’re not used to making changes to the php files – http://www.themecustomizers.com/