Aoallis asked me in a comment about how the boutis is finished. There are several possibilities, all are described in the various books on the boutis.
1. You can hem the edge after completing the stuffing. To do this, trim the fabric to about 1/2" all around then fold the edge down twice over the last stuffed channel. Then hem into the "ditch" formed by the last line of stitching.
2. You can finish the edge with an embroidered scallop. To do this, draw an additional line outside of your design about 1/8-1/4" , stitch this and stuff lightly, then using a very fine (Cordonnet No. 80 by DMC) white thread, buttonhole stitch the edge very closely. Do this before stuffing the channels of your work. Then complete the boutis, wash the item and very carefully trim away the excess fabric.
3. You can also finish the edge by folding both the front and back fabric to the inside and slip stitching closed, then stuff the channel made by this.
I will try to post some photos later with some examples of the above, but in the meantime please refer to the books on the subject if you have access to them.
Happy stitching !