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?