Is this inside the shower or outside? Where is the waterproofing? Curb cover is typically the last piece to be set.

I need a much better pic showing what you are talking about .Post it here in a commment DO NOT start another post.

Nobody understands the question. Show the entire bath, and what has this bath floor to do with the whole house flooring? Is the shower to have doors? Is the low threshold your curb" It is supposed to be walk in and is the gap temporary, or when the floor IS installed there will be a slight gap???

Is that the issue? ( Your floor does not appear to be level ) but the floor isn't installed, there is NO thinset beneath as of yet.

Set it correctly, first of all.

For the picture, pick up the cloth and show the shower pan in relation to the floor. I am thinking that you have a Kohler cast iron shower pan or other one-piece shower floor already installed, right?

Why, in the first picture, is there such a gap between the hardibacker and the edge of the shower pan? Is the last picture of the hardibacker and shower pan, too, or is there something else on top of the hardibacker now? The gap is gone here. Is the floor that out of level that there is a 1/2” gap on one end and the tile is covering up a smaller 1/4” gap at the other end?

My roll-in shower pan meets the top of my floor tile within about 1/8”. The gap between my soldi-surface pan and the components that make up my bathroom floor was filled with something that I think my contractor called Kerdi Fix. I have a Kerdi waterproofing system on my bathroom floor. Kerdi Fix was used where the backerboard and Kerdi membrane and floor tile meet the front of the shower pan to make a waterproof joint.