If you zoom an image in the Photoshop Elements Editor, parts of the canvas become hidden when they extend beyond the edge of the workspace. However, it is not always obvious that this has happened so you may be unaware that you are not viewing the whole image.
Currently when this happens, a truncated edge of the canvas appears the same as its true edge (both marked with a thin black line). I suggest that the canvas should be displayed with a border around it, so that when the canvas extends beyond the workspace, the border will be hidden and make it obvious that the view has been truncated.
If you are making a feature request, you are probably not going to get much traction in this forum. I've been using Elements since its first versions and I don't think I've ever seen a complaint about the issue you are raising. However, I'm not saying it is not a valid request.
And in case you are not familiar with the keyboard shortcut, Ctrl+0 will fit the entire canvas on screen.