Built-in bathtub with tiling

So basically I’m redoing my bathroom. When I tore out the shower surround and tub, I discovered that whoever remodeled this bathroom years ago cut an inch of stud so it would accommodate a standard 60 inch tub. The bathroom is a little over 59 inches wide, so apparently that was their way of installing the tub. I figured that on the side where they cut the studs, I would just attach 2x4s to the cut studs to bring them out above the flange. That way the door panel will be pretty much flush with the drywall.

Obviously the biggest downside to this would be that if water were to get behind the tile and board, it would most likely get behind the wall it is in. I plan on extending the control panel and tile about 6 inches beyond the tub apron to help with the drainage of water that is also coming out of the shower.

I can’t reframe the wall because it faces another room and it just wouldn’t be possible for me to do that. How screwed am I that I can’t make this work and make it as watertight as possible?