percentage width 50% and 50% showing as one column

I installed the plugin, it’s so good, thank you very much for sharing it

When I try to set the column width at 50% (I want it to look good in all devices, I’m using responsive theme) it doesn’t work. It shows only one column.

Thank you in advance for any help you can provide.

http://wordpress.org/extend/plugins/column-matic/