Ah that sounds as if you had a background set in the Environment pane - if it was a solid colour that would have made a rectangle (though it should not have shown up unless you loaded a sceen with that set up - you can't, in 4.9, 4.8, and possibly 4.7, set the Environment persistently between sessions).

I suspect that the offset is not that the camera is misplaced but that the render aspect ration (as shown by the frame) is wide compared to its height - render size does persist between sessions, it can be set in the General group of Render Settings>Editor tab (you will need to turn Constrain Aspect ratio off first).