I suspect it has to do with how the CSS widths of the columns are configured. For example, the div you placed the shortcode within should not be set to 100%. You could set the width of the sidebar and set it to display as an inline block or float it. The same for the container div, but you would not set the width because you would want it to fill the remainder of the width.
Here’s a link to a basic CSS column tutorial.
The cards themselves will take up the full width of the container they are within.
Hope this helps!