Thanks a lot for the hint EdLoach!

I made a completely new way over it and deleted the old one. This should fix it, I hope.

Thanks for the comments.
The walking papers would not help to get the really small roads. They are very labyrinthine.
Walking papers would help to get the shops and cafes, but that would be the next step.
Sure, balloon photography would be great. But I am there only 9 days per year, this is infeasible for me.
My last idea is to ask the local tourist office to allow me to use their old-town-tourist-map for OSM.