Sometimes we don't have the right image immediately in the shooting. What I always tell to my students, during my workshops, is to see over the shoot. You can get your goal mixing different parts of pictures to reconstructing what you've seen in your mind. In this example I had a beautiful shoot (left image) but unfortunately it was cropped, because it was in landscape format, and on the right side, the second image, I had a good figure on the bottom of picture. So I decided to mix the first picture with the second, to obtain the right result.
And this is finally the final image. The results are absolutely real, and you can get the image you love.
Compositing help us to obtain results that are not possible at the first sight. Don't be sad... while you're shooting, a careful eye can see where others peoples can't... This is the key.