Hey Greg,
What happens is the Stack’s CSS loads first (2 columns default) then the Woo Checkout Editor’s CSS (1 column via the form-row-wide
class. The Woo Checkout Editor CSS needs to load first in order for the 2 columns to not take effect.
Regretfully, there is no solution to that but to reorder the loading of CSS. It is WordPress that loads the theme’s CSS first then the plugins.
I’ll submit this in our issue tracker to see if our development team could come up with a solution to this but using a 3rd party plugin or have a personal developer re-order the loading of CSS would be the solution. You can look up in the WordPress repo or premium WP marketplaces for such a plugin.
Thank you for understanding.