2nd column (of 2) starts below and to right of 1st

Hi — I love the simplicity of this plugin, but am having a problem using it for the first time. In a basic 2-column layout the columns are created correctly, but the second one starts below as well as to the right of the first.

In case it helps, it also appears to me that the left hand column is inset to the right a bit, which it should not be. (I’m assuming the plug-in isn’t meant to change the margins of the text area being split into columns.) Here’s an example page:

https://rowantree.benwolfedesign.com/about/

I’m using the Headway theme.

https://www.ads-software.com/plugins/grid-columns/