Charlie, I have this same clematis (also blooming right now!) and it does leave you wondering what to do with the composition. It's such a square shaped flower that I often end up giving it a square crop.
I like it as presented...might try to blur the BG even more to make the lighter and darker tones swirl together a little better but that's a minor thing. The diffused light is nice but think you could also increase the saturation a tad if you wanted a punchier image.