Hey! I don’t think what you did is wrong; it actually looks good. That said, it’s ideal to build a solid drawing foundation and have a good understanding of the torso muscles (and anatomy in general) so you can better understand their volume. Volume is the key part; you don’t need to be a master of anatomy. For example, the area right below the chest shouldn’t be entirely dark, since it shares volume with the abs. Because of that, we should still see some light hitting the upper part of that area. Usually, 3/4 lighting, or a 3/4 pose, helps describe volume more clearly. This is just an example, and the same principles apply even in a front-facing pose. The main point is to keep the basic forms of the muscles in mind, whether you think of them as boxes or cylinders. This will give you a much better sense of how to light them. Hope this helps! :)
