I like Magnum as a bittering hop in my German beers - a lot less vegetal for the same IBUs. Also the yeast really needs to be Bavarian. Of course a Munich boiled water profile, too. Finally, consider a single decoction and you should be there, but one friend made a great one with a little Melanoiden, instead of decocting. Good fresh ingredients from the continent is a must, too. I have not used American ingredients in my German lagers for quite a while and would not go back.
Just keep making it over and over and you will dial it in for what you like and have a lot of great Dunkel! (But you already knew that).