I think you are doing great.But being an artist myself, I think that the post that said go for the lite, med and dark value is rite. You just need to use a little contrast in the darker areas. Just my thought. Some one else on here did something like that and when I asked about the shading, she said she used a little shading with a diluted paint. Just keep going, you will do fine. Takes time and you are to criticule of your own work. Walk away for a while. I have to do that when I am painting. Especially if I am trying to hard. Which I am sure you are doing. Keep it up. You aren't done yet.