Once you are satisfied with the number of flower stems (I have used four so far) shorten the stems using a sharp florist knife.
Cut the stems all to the same length. Take care not to crush the cell structure.
There was one stem that did not stay in place to my satisfaction.
I inserted a pearl headed pin, carefully pointing it down, concealing the point in the other flower stems so it doesn't present a hazard to human hands. The pin satisfactorily secured the calla, making it stay in the right place.
I'm now going to add a Ti Leaf to the right side of the calla lily and taping it into place.
Face the leaf inward, surrounding the lower calla on the right.