< I have some problem with the English language
What languages do you want? :)
There are yet 3 possible in this forum :)
English Spanish French :)
About the rail : you have not make error!
Just your curves are not adapted.

A cool management can be this one
Make you sweep with 1 or 2 rail
So you can now draw the rail measure over your volume (better if it is snapped at the extremities
Select your previous volume sweep
Erase it : so you have always your curve + 1 or 2 rail and the Rail measure
Now you can make the complete Sweep + Rail Measure :)