In the widget editor the layouts align exactly, however when using it in the main editor the children within the widget switcher get resized, i.e padding on the right gets extended.
This progress bar seems like it’s going to take the entire screen - this is just a preview, not the final result. The final result will become more clear once I add this widget to another container - then we need to consider what that container is sitting inside of… this whole thing trickles down and revolves around Desired Size which children can report and parents can, optionally, respect or ignore via alignment settings of the slots they produce.