So I have put hardibacker on the walls around the tub and on one of the three walls the wall is not flush with the tub flange (See pic below). Not sure how to make the wall a bit thicker to go over the tub.
The Hardibacker or cement board should overlap the tub flange down to about ¼" to ½" above the tub itself. Then bring your tile down to around ⅛" from the tub and finally caulk that joint for a good seal.
The way you have it now will fail and allow water between the backer and tub and into the framing. Gaps to be caulked should be kept to less than ¼" preferrably ⅛" or less.
Normally, the tub fits quite snug into the opening in the framing. Then the cement board comes down over the flange on the tub so if water gets through the tile (and it will at some point) it drains into the tub. Water will wick into any crack you give it and seep into undesirable locations.