I tried again to do the same assignment, but this time, the drawings are more 3d

Most noticeable issue I see is flatness. Your 3D doesn't look very well done. 3D is a hard thing to get used to for beginners so I recommend this playlist: https://www.youtube.com/watch?v=gq87eOmS4Wo&list=PLMXbAPr21di8ARBkUTkho1YNq4O7h0wyQ It should really help. That's all.