Beautiful looking Clematis. Unfortunately I think the lighting is a bit flat and slightly underexposed. A boost with a levels adjustment layer could really have helped in this regard.
Concerning the composition, I do think the two petals to the left of the frame are a little bit distracting. I personally would favour a square crop for this specific flower, I think the flower would suit that kind of framing.
Clematis! Great year for them here; very profuse blooms. Nice shot of it; I might rotate a bit and crop tighter on the left to get rid of the bits of petal there.