This is done beautifully! Do you have underdrawing? or simply build on top of previous drawn shapes?

Nice drawing Mathew, your lines look very confident. If you're trying to get those shadows to pop, take the leap and make them darker! Having that light/dark value contrast is what will give your drawing a sense of part of the form being in light and part of the form being in shadow. As it is now in your drawing, everything feels like it's in light. Of course there can be subtlety in shadow values with things like reflected light(For example in your reference, there is light, core shadow, and parts of the shadow are slightly more illuminated by reflected light from whatever surrounding environment) But more important than that is the idea that we're trying to group lights and shadows to feel separate. A very general rule of thumb, (If you are wanting a strong light/shadow contrast) that you should keep your lightest shadow a darker value than your darkest light. Hope this helps a bit, I look forward to seeing more of your studies!