Place single pins all around at first to be sure the tulle is exactly how you want it. There should be no folds or wrinkles in the fabric.
Use a lot of pins to pierce the fabric and keep it in place after the excess is trimmed away.
Using sharp scissors, cut away the excess fabric, leaving only the round bottom covering of tulle.
Here is a closeup of how the finished bottom should look.
You are now ready to start creating the tulle puffs that will encircle the bouquet holder.