Elementor: merge sections

I am struggling with designing a page using Elementor. I had created some sections, and then decided I’l like to combine them into one so I can add a background behind all of these particular sections. I’ve tried an inner section, removing one of the default columns (so there is only one), and dragging my other sections into that one. In a nutshell, it only allowed me to drag one section (a header) before reverting to two columns again.

Thanks. I can’t find a solution anywhere!