Looks to me it was well worth the 20+ hours. It's stunning!
I'm assuming your using painter? There's a painter thread here you can look at and ask questions. Can't help you much other than that, I'm just learning painter myself. What I usually do is zoom in, and I use the knife alot, then refine from there. The more experienced here will probably tell you a better way, I'm used to painting with real paints and it's the best way I've found so far to emulate real painting.
Art gives me a life of extreme challenge, frustration, accomplishment and contentment. Nothing less will do!