If nothing else, sounds like you need to perform the trace rotation which is a screw trim adjustment which can be accessed from the front panel between the Focus and Readout control knobs just under the CRT face. That adjustment should allow you to get the trace even with the "horizon". If there is also any "bowing" on the trace you might need to perform the Geometry adjustment first, which as far as I remember is inside the scope. I don't have the SM manual handy so best you take a look into it. Manual is available here:
