Should be "column_2" (lower case "C"). Try it to see if it makes a difference.
http://help.machform.com/m/using-machform/l/556236-adding-columns-to-your-form
If you want two columns, add column_2 to each field to reformat as the two columns.
Note you won't see the change in the form editor, only when you view the site.
Just mentioning the above (even if obvious) as you might have overlooked something.