It looks overexposed and the magenta/pink is oversaturated. I avoid magenta because it is the most difficult color to work with. It seems to not have much forgivness in it as far as color clipping goes.
I like the idea, i think - compositionally, though I'm not sure you've quite pulled it off - perhaps the flower's structure just isn't regular enough for the image to handle this partial treatment; that trick usually seems to depend on the viewer having the impression that the object is so regular there is simply no point in including the rest of it. I think also there's something amiss with the intensity of these colours - over saturation, or simply over-exposure (I'm sure you could have exposed a stop less and had more impact)? The pink certainly becomes kind of messy and indistinct toward the centre of the flower.
at first glance I though of this as just another flower shot, but looking again I realize that this flower looks really really really WET and the brilliant coloration is just the sort of thing that happens after a rain. in other words, you meet the challenge very well.