Your theme is responsible for wrapping elements in accordance to how the sidebar is output on the page. Just to be sure, I searched through all the code for ACFW and didn’t find a single <section> or <aside> element.
That said, you should be able to use CSS to achieve some sort of full width for your widgets. If you can’t use the general width: 100% idea, I would look into using negative margins and positive padding. CSS-Tricks has a good article if the full width is being used to set a background that spans the width of the screen. https://css-tricks.com/full-browser-width-bars/
I would recommend reaching out to whoever made your theme and working with them to find out how to get your ideas into the browser! 🙂