When making a tiny stem, I cut a strip on the bias bigger then I need. I fold the strip right side out, pin it to the shape I want and hand stitch 1/8 away from the folded edge to the background. Some trim close to the hand stitching, fold the fold edge over the raw edges and hand stitch the other side down.
I like to instead of trimming the edges close to the stitches, I leave a little extra and fold in the raw edge towards the stitching line and then fold over the fold edge and hand stitch the folded edge down. It makes the stem a little fuller but is easier to make sure the raw edge doesn’t peek out of the hand stitching.