I think you need to do this as a series of 2 rail sweeps. Your long curved lines will be the rails, you pick 2 then your U shape will be the controlling vector for the shape. I believe that the order in which you select your lines is important and also you have to have points at the same end of both lines. Not sure how to explain that, but it looks like you don't have that therefore the weird pattern. I'm not in front of the program, it is down at the companies office so i'm quoting from memory.