I'm a beginner trying to teach myself Solidworks with the help of a textbook. I've drawing a contour which looks like it's a closed loop. I tried doing a Revolved Boss/Base using a centerline as the axis of revolution. I get an error message that says " Sketch is open, self-intersecting or intersects the centerline." The contour looks closed to me and is just touching the centerline. If not touching, the revolved object would have a hole in the center which is not what is desired. What am I doing wrong?