I think you're off to a good start, the proportions just need a little bit of tweaking.
I think a good first step is to ditch the lines, start with a silhouette, it's much easier to see issues, and fix them in a silhouette. You can just sculpt away and add freely without worrying about messing up your other lines.

The second thing I want to mention is a little tip for drawing organic forms. Organic things, especially things with muscles and joints, usually follow a certain flowy pattern.
I often find that a good guide is to think of it as a curvy line, where each curve gets a little tighter towards the end, usually in a pattern of BIG Medium small. I've drawn the curves that I think of in the last frame of the gif.
The yellow curve is my way of getting the height proportions down, first curve is the head, always a good spot to start. So the head is the small, the chest is the Medium, and the legs follow suit and become the BIG.

On the arms and legs you'll notice I've drawn 2 curves, when overlapped youll see theyre sort of off from one another. The flow of muscles follows this curve where it's sort of a balancing between inside and outside curves. For me, it's best to think of them in pairs of high and low curves. The green lines I've drawn represent the low curves, and the red the highs. If you look for example at the thigh, you'll see that the outside curve is way higher than the inside curve. Then as we go down to the knee it switches, so the inside knee is (it's not actually the knee it's a continuation of the quadriceps called the vastus medialis and the vastus lateralis), then switches again at the calf where the outside is once again higher.
Anatomy is definitely tricky. The way I draw bodies is a little bit of personal preference so don't take my example as gospel. The best example you can get though is a real human so feel free to pose and take pictures of yourself (there's also great websites with models for free, but often to get the pose you want it's best to take it yourself).
Edit: I should also mention that this applies to (I think) all body types/body sizes/genders.