Did you also set it under “Estatik”, “Settings” and “Layouts”?
Personally, when I use that shortcode (“[es_my_listing layout=”3_col”]”) it shows up as 3 columns unless my browser is set narrower (then it only shows up as 2 columns)…
but even without that code (using this instead “[es_my_listing category=”For Sale”]” it shows up as 3 columns when the third layout is selected in the settings mentioned above.
Hope this helps.