Very good videos from Model Mania, especially like the shortcuts for creating keyholes, right click on mouse while hovering over a surface to reveal the bottom side of part instead of rotating view when adding mates. Now can't figure out why, using the Contour Selection Method over Traditional Method, my sketch 1 isn't good when creating the 12mm high extrusions of those 3mm offsets. I've check the net zero condition and don't see any as all arcs have tangency to the 3 circles.
Looks like daylight between the flat and your sketch, and contact in two points. This would make zero thickness geometry.