Not bad for a first try! However there are a few things I noticed right away:
Your WB seems off
Iron your backdrop so the wrinkles aren't distracting, then take a step or two foward to distance yourself from the backdrop. An larger aperture (f/8-f/11) will make the backdrop less distracting
As a personal rule I use, I would say don't cut off limbs or part of someones body unless doing so for compositional purposes. Here, cutting off at the knees will be annoying. For most portraits, either do full body shots, waist and up shots, or headshots to avoid this.