We all stink at first. The good news is that you can just keep after it until you get it right. Sometimes, you just have to walk away for a few days and tackle it again.
One thing to remember is that the texture of body filler is different from metal. If you don't want to see the body filler, you'll have to sand it with 600+ grit. Even if everything is perfectly smooth, you still may see the body filler due to textural differences unless you are patient enough to sand (and sand and sand and sand) with the fine grits.
Good luck!
