This doesn't have to be an "exact" science. The two ends should be lined up, but they will be snipped off later at either an angle or a "v" cut.
If you look on the underside, you'll see the folded tulle is about the same width as the #40 ribbon.
It is easier to twist the bow if the satin ribbon is on top rather than on the bottom.
I give the ribbon and layered tulle a sharp twist, as shown below.
You can see that my index finger and my third (middle) finger are holding the ribbon in place, while my thumb and fourth finger hold the first portion in place.