All this historgram is showing is that you streched it too much. Typically this is leading to banding in the image. If you dont see banding, you are good to go. If you just worried about the historgam you can add a bit of (color) noise and et voilà 
All this historgram is showing is that you streched it too much. Typically this is leading to banding in the image. If you dont see banding, you are good to go. If you just worried about the historgam you can add a bit of (color) noise and et voilà