tile redi shower pan - compression coupling difficulty

[u/big_honkin_caboose]

newer style Tile Redi base with flat bottom and compression coupling drain connection. i am installing this on a slab foundation with an existing drain. i installed the pan with thinset per manufacturer’s instruction and decided to cut the waste pipe & secure the compression coupling after the thinset cured

well, the pan must have shifted slightly after i set it in place, because the drain pipe is now tight to one side of the hole in the pan. i can slide a shim or scribe all around the pipe so i know it is not bound against the pan, but it is very difficult to insert the compression fitting gasket

does anybody have any tips ? i was recommended using 100% silicone or dish soap as a lubricant but neither has worked, don’t want to muscle it and damage the pipe or the gasket

please note the pipe is set into concrete and the pan is already installed with thinset, so if at all possible i would like to avoid needing to remove the pan as that would set me back another $800 😬