The main problem with the values is that they're boring. You can adjust the design of the original if you want. This is pretty flat and you main problem is the proportions. You've overfocused - a classic mistake. The best way to remedy it is to work in stages - sketch first, ensuring the proportions are correct, go slow, be very patient. Then place in the shadows, just draw them in with a pencil - find out about terminators, there's a lesson on Proko's channel about this, called mind blowing shading tricks. Then just go slowly, adding colour, smoothing out plane differences where they need to be, practice on another sheet of paper or on another file if you like, then, when you've done that; sleep on it, take a break, look back at it with fresh eyes, then correct mistakes. Don't re do the whole thing even if you want to - finish it first at least. Then add special effects, highlights, and grainy textures if you want or need to. You can probably work a process out for yourself. Even if you're just copying, you do seem to have some control over what you're doing.