Hi Graywolf
I'm not entirely sure what is is you would like to achieve, however I'll go out on a limb and assume you would like to get away from the line drawing appearance of your reference image, and that you would like something that is a little more realistic with some degree of depth and including muscle tones and that sort of thing.
If that is the case, I should point out that the only way to avoid the stenciled look is to avoid using stencils, or at the very least to make it less evident, I personally would only use stencils to apply a light mist to get my proportions right, I see that you have cut your shapes out of the stencil leaving behind the line drawing part of, this would have been more successful on a black background.
If I wanted to do this myself, I would have cut more stencils, the fist of these would have been a stencil the shape of the whole image to the perimeter, using this I would spray a light mist just enough to be able to see the shape of the whole image, the next stencil would show the key points, the lines of the wings, wing root, mane tail including a little hair detail and eyes and hoofs, again I would spray very lightly with black or a dark colour enough the see the key shapes, the rest of it O would simply freehand, although i would reuse the first stencil to avoid unwanted over spray.
On the wings you sprayed the lilac evenly, this would have been more convincing if you had blended going from dark on top to lighter on the bottom, this would give some depth and form.
I would suggest looking for a reference that is closer to what you seek, although I generally look for more images that can study for important details, unless you have Pegasus in your back garden,
, it's hard to produce a 3D looking image out of your head.
Basically the process you would use is similar to that for doing portraits.
So do you have any suggestion for me to do so I can get away from the stencil looks. And Thanks In Advance
