If it will bother you every time you go in the bathroom and see the shower -- then stop the work and have this resolved. That said, your GC should have brought this to your attention earlier. Its possible he didn't want to cut a joist (but he most certainly could have, and added more bracing). In any case, the costs will be to demo the mud bed (and install a new one), and certainly plumbing and possibly some carpentry/framing. I had an issue like this with my kitchen. I came home and there was a tile problem. For a couple of hours I went back and forth -- could I live with it. In the end, I spoke to the GC in the morning, had it torn out and redone. We split the cost. Every time I walk into the redone kitchen, I am SO pleased with the result - and this problem would have spoiled it. The cost will not he insignificant, but against your total budget and for your enjoyment, I would say have it changed -- even if some of its on your nickel. Pete

Spoken like someone who is receiving rather than writing the check! :) To me it wasn't worth jackhammering in the bathroom to move the drain a couple of inches! In terms of both the cost and the mess it was never a consideration. If the offset was more extreme, I imagine we would have gone the jackhammer route. I've never been convinced that a drain has to be in the exact center of a shower anyway and truly never notice the offset. This was a "medium/refresh" remodel, not a total gut: new countertops and fixtures, new wallpaper and pulled the fiberglass shower out to put in the tile. We kept the floor and cabinets (fresh coat of finish and new knobs). Any money we could save was welcome and any dust and mess we could keep at bay made me happier! We spent hundreds more on the french doors because I wanted that look, but I wasn't willing to spend any money to move the drain.... Since the money tree only blooms occasionally for most of us, it's all about the choices!!!

You are not going to notice the floor slope whether it is all in one direction or comes from both sides to the center. As for whether you put the drain at one end or in the center, I think either would work. The only points I will make are that: 1) If a curbless shower is to be used by someone with a wheel chair, it would be better to have the drain at the far end from the entrance so it doesn't keep getting rolled over repeatedly. 2) if you have a drain in the center, then you have to only provide half as much difference in height for the slope to the drain compared to having the drain at one end. This can be important with curbless shower installations if there are framing or foundation problems that restrict how much you can lower the shower floor compared to the bathroom floor.

moving fwd youll need a 2" drain rise and trap. depending on if this is a slab on grade, or wood structure will effect how easily thats achieved, post tension Condo slab even more tricky etc. When choosing linear drains one must very clearly understand A bonding flange linear drain VS. A Linear drain strainer and know how to select the proper drain and waterproofing. Id suggest focusing on a smart hiring decision start asking the tile pros on here HOW to hire the right tile crew rather than technical drain concerns.