you definately done the right thing..i always check if the walls etc ceilings are running off ,,the only thing that matters is that your tiles are set level from the start even although the gap is bigger at one end you can see the tiles are level,,if you had followed the wonky ceiling line your tiling would have been messy to say the least,people can see from your pic that its the combed ceiling thats running all over the shop whilst your tiles hold straight lines,,nice one
one further thing to check though,,say you had 2 combed ceiling sides always check where your trim is going to be at the top of your tiles that the wonky rollercoaster ceiling line isnt going to drop on the other wall and hit your tile datum line so to speak.
had a similar job last week,,a bethroom with 2 combed ceilings which were terribley off,plus had to drop a cut into a boxed in bath whilst makin sure i had a good sized tile running behind the sink etc,,if you dont take your time planning it out like you did today youll end up wishing you had.