>>3419755 If you point camera up or down, vertical lines off center will not be vertical any more and if you tilt camera to "fix" it you get tilted horizon.
Avoid tilting camera. Get horizon on level first and then worry about vertical lines. If want to shoot up / down, without tilt shift lens you either live with it or use perspective correction tool in post.
Just a sketch of possible edit. Rotate, adjust pespective (and do it better than I did) and crop edges.
