Occasionally, a gremlin of some sort will find its way into your site, and the full-width section you’ve so carefully designed in Elementor will stubbornly refuse to actually be full width. Instead, it will have a gap around the edges.
This is a very simple fix, but people often apply it in the wrong place.
Click on the section’s Section tab (not the Column tab), and set the column gap to NO GAP. Don’t let the phrase “column gap” mix you up. You need to the set the column gap on the Section, not the Column. See the screenshot below: