Looking at the pic of the quilt, see where they have HALF a cone at the end of every other row? That will even out the rows.
Now, looking at the colored line drawing, where the TOP of two curves connect, that intersection will match the point of the cone in the bottom row.
So, I would cut out one cone, and put two rows together and see how this works for you.
Pinning is important here. Use pins to match up your "points" before you sew.
Hope the helps a little.