I wish I could offer some advice to help you, but I too am in the same boat most of the time. The most stressful part is when it is time to apply the color and finish. One false move and BAM, it is ruined.
I am the same way with charging for my projects as you. I charge what I think is fair to me and low enough it might sell. I do mostly custom work, so an estimate is given up front. It mostly works out. I didn't get into this to make money, it just happened. I still have to pinch myself at times to think someone wants to buy what I do.
Quick question. What tool was used to do the background around your leaves?
Again nice clean work you did there.