Most shower doors are made to allow for this very situation. The pivot system does not allow as much though.
I would consider not using the pivot system and get the piano hinge system that has a sleeve on each side that you adjust to uneven walls and mount accordingly.
You follow the contour of the walls on each side, but the working part will adjust to complete levelness.
you need to shop around and study the directions in each product and find the one that allows for the most off level walls.
Do not fret. No walls even on a $1,000,000 home are level. these things allow for that.
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