You see extra/unwanted margins from rows when you use the post content module in a Divi theme builder layout for posts and pages.

You can set the row in the Divi builder to 100% each time, but it’s easier with a single CSS setting:

/* -- START Fix width of rows inside the Post Content module -- */
.et-db #et-boc .et-l .et-l--post .et_builder_inner_content
.et_pb_row {
width: 100%;
}
/* -- END Fix width of rows inside the Post Content module -- */Code language: CSS (css)

Source: https://www.peeayecreative.com/how-to-fix-the-divi-theme-builder-post-content-module-width/