Divi has build in gutter widths:

1 = No margin
2 = Margin of 3%
3 = Margin of 5.5% (default setting)
4 = Margin of 8%Code language: JavaScript (javascript)

If you want a gutter that is smaller then 3% you can do this with the following CSS

Add the following to the ROW » advanced » custom css » free form css and change the value as needed.

selector .et_pb_column{
margin-right:16px !important;
width: calc(100% - 16px) !important;
}Code language: CSS (css)