Bath tub not against wall advice

[123jemzzz12]

Hi all, new to this and asking for advice. I am renovating my first home and it's not been a smooth ride so far but have picked up a decent amount of trade skills I didn't know I had haha. However slight hiccup with my bathroom, stripped the bottom half of the wall of old plywood fake tiles circa 1960, found timber cladding, removed timber cladding, found old lath and plaster crumbling wall circa 1920. Not great fun! Removed and replaced plasterboard and taped and filled, all ok. Ready for tiling. Now once wall is tiled i have measured that there will be about a 1.5inch gap between the tile on wall and the bath edge. It is an old steel built in bath with questionable old plumbing so really not wanting to open another "can of worms" by moving bath and waste, but need an alternative for this gap as can't obviously have water going to here from the above shower. Plastic edge bath seal fitted would steel leave about an inch gap...I'm thinking of boxing in the gap and tiling it and making it a ledge, but again would prefer if any pvc alternatives or any ideas to save the hassle... many thanks in advance!