How to correctly set walls?

I've been having trouble with the walls in Complete Circuit Builder. I'm trying to get a wall so you can't go off the road (into out of bounds) but when I try it normally, I go right through it and can't get back on the track. Can somebody help me with this?

I had that sme problem that you are having, what you need to do is make the inside, and then on the outside, make  it so that the track is the only thing not shaded. You do this by going and making the walls go to the edge of the image and running along the edge, and then cutting back to outline the course.