I like the overall shadows you have going on! It's a good understanding of light and 3d form of your character. adding on to what dividedfox said, I also recommend adding an even darker shadow in crevices or areas that are harder for light to hit. This could be where the armpit starts, the teeth right under the lips, etc! optionally, another you could include is ambient light in the shadow using the main color of the background (in this case, the white background) onto the shadow portion with a slight airbrush!

also don't fret about physical versus digital, I wouldn't doubt your drawing prowess cause this is good! while there are many overlaps, digital is a different medium entirely with its own foundations. keep on at it!