Osaka - I had the same problem at first, but I think I have it figured out now. The last part of step three says to click just inside the perimeter to turn it into a selection. For me, if I don't click in just the right place, it adds another point rather than changing it to a selection. I can find just the right location to click by watching the pointer. While making the points, the pointer is an arrowhead, with the scissor icon below it and a cross next to arrowhead. When I'm in the right location to make the selection, the cross disappears. Sorry I don't know how to explain this more clearly, but I hope it makes sense.
Osaka - I had the same problem at first, but I think I have it figured out now. The last part of step three says to click just inside the perimeter to turn it into a selection. For me, if I don't click in just the right place, it adds another point rather than changing it to a selection. I can find just the right location to click by watching the pointer. While making the points, the pointer is an arrowhead, with the scissor icon below it and a cross next to arrowhead. When I'm in the right location to make the selection, the cross disappears. Sorry I don't know how to explain this more clearly, but I hope it makes sense.