Too much left and right margin (15px)

On my website there’s an extra 15px left and right margin.

#pg-17-0, #pg-17-1, #pg-17-2, #pg-17-3, #pg-17-4, #pg-17-5, #pg-17-6, #pg-17-7, #pg-17-8, #pg-17-9, #pg-17-10, #pg-17-11, #pg-17-12, #pg-17-13, #pg-17-14, #pg-17-15, #pg-17-16, #pg-17-17, #pg-17-18 {
margin-left: -15px;
margin-right: -15px;
}

I believe this is caused by the 30px space between rows (adjusting for this by -15px and -15px). I can’t remove this, because then there’s no space between rows. Do I need to edit something in my theme files / siteorigin CSS.

Thanks for looking into my problem. For this site I don’t need premium, but I think I’ll buy it to try it for the custom template function.