Dear Joann,
You don't need to increase difficulty by doing movements not called for. The way you increase the difficulty is how you plan the freestyle. If you did a zig zag leg yield and showed your horse's suppleness and ability to change positioning easily, that would increase the difficulty. If you did trot canter, trot canter several times in different patterns to show how you could take a movement or series of movements required and increase the difficulty in showing it, that would increase the difficulty. What you don't want is a freestyle that looks like another first level test. That is the hard part of planning a freestyle. However, the technical part of the movements and doing them well and a good plan with appropriate music that highlights your horse makes good freestyle, not doing something poorly to "try" to show something you and your horse aren't ready to do. Don't make it unreasonably hard as you can really mess the whole ride up that way. This is to showcase your horse's strengths and learn by doing it and by having fun. As in riding any tests it helps to increase your ability to see where you need to do your homework and train harder.
I hope that this helps. Maybe I can look up some things about freestyles also to bring with me.
Linda