[Plugin: Smart Post Lists Light] How to control output columns

First of all I’d just like to say this is a great widget.
I set it up in a project on local host and it worked perfectly.
Now that I’ve set it up in a live environment the posts have arranged themselves in three columns instead of just one.
I’m using the same template in both projects.
My live project is https://www.activityneeds.com

I’d appreciate any advice on how to fix this problem.
Thanks
Will

https://www.ads-software.com/extend/plugins/smart-post-lists-light/