I think you did a great job, LPS. With some practice, I'm sure you'll improve quite well!

I think this looks fine. I don't see anything wrong with it, and I'd rather not have any mistakes pointed out to me. Good job on this ^^

I personally understand your problem very well, sometimes the simplest sketches are the hardest for me to make.
If you did this in sharpie or some sort of marker , I must say that this was some very impressive coverage of the whole body, I can't see any white spots or patchy marks.
Maybe next time you can try shading the white areas of the body for a more interesting effect?

Steele's neck is a bit too long, and his muzzle is shaped kind of like a dolphin's nose. I would suggest that you look at pictures of real dogs to help and improve your art.