Hello, You see it that way because you defined the direction of the stair exit line in reverse. You can define it in the other direction and try again.
The message you get is not direction related. You should keep a point directly above the outer contour with the nearest point or midpoint. You will get this error even if it is slightly inside or outside the contour. The output line should be just above it.
building load. 3m naturally, the difference in elevation between the first step and the last step of the stairs should be 3 meters, so is it enough for me to look at the 3D view to understand the accuracy of the elevations of this staircase I made?
In the ladder settings / areas tab; for the last arm, you can check the last step at the upper level option and look from the perspective. There is no need to re-route.