Hi Michael,
The curved wall is part of a tramcar model body. Normally, I draw the floor lines in distance of wall thickness, connect both side ends with lines and extrude to the desired height. Alternatively, I draw the vertically profile of the wall and drag it along the floor plan (sweep).
Also, I have already cut out such a curved part from a block and all other methods given by Moi.
In all cases, the course of the inner and outer wall surface is not identical to the given curves. This has nothing to do with a mesh because the error is already visible in the 3dm file long before creation of STL file.
When you zoom in on the view from above, you can see a gray area next to the given lines (red and green) that indicates the "wrong" course of the wall. This wrong course will be shown also in STL file, that's clear.

Bodo-Lutzt