Why is 3-column grid becoming 4-columns?

[user198]

This is set to a 3-column grid in the editor.

But when I publish it the grid size expands to 4-columns:

[loeiks]

In the editor you have a screen size width of 1280px but when you open your website you will see it in 1920px width so what you can do is change the min width of grid columns. You can also add some grid-gap (spacing) between every grid column.

Let me know if this works.