To make stitches look fuller or more rounded try a Smyrna cross stitch. This is a closeup of the stemmed cherries at the bottom of the Chocolate Covered Cherries.
I ‘plumped' these tiny cherries by adding a + on top of the x stitch to make them look fuller and more rounded. The photo is a bit fuzzy but I hope it shows the difference between the red cherries at the bottom of the stems and the green x at the top. By adding a horizontal and a vertical stitch on top of the diagonal stitches of the initial cross stitch a Smyrna cross stitch is formed! I use this stitch when ‘rounding’ out an eye, for example. The top stitches can also be done in a different color for subtle shading or bright contrast.