We could just add 3 knots, but that would add 27 more control points that we can do without. The key to a good clean model is to have as few control points as you can. Move the slider up to 10. Take a look. As you can see, we just put a crease in the surface with 9 points that would have taken 27 points to do.
Lets add one more twards the bottom of the surface.
Select all the control points on the 6th row, Like this. In the top view. Drag the slider up to 10. So when you adjust the point weight, only do it to the points needed and not all of them. Well, That's it.