"What to do?"

How big old boy is the contractor?

Big. like Boagrius from Troy big.

Well that eliminates an ass wupping so we'll need to come up with something else.

It looks bad. I wouldnt be using that shower. I am betting, he didnt waterproof properly either. Hopefully, you havent paid him, because, it really needs to be redone.

Bull Nose Tile

Have some leftover tiles. thinking of cut and paste and then sand the edges for a bullnose look/function. Wonder how deep of thinsets I need to remove from the gaps for a good bond.