Since I am not you I can't really tell you how to feel. But there are two sides to every story and we all at times get really
about the small things in life, and that its more about the principle than the money. But, consider this, you are just getting yourself worked up over a few hundred bucks at worst and a miscommunication. Not worth it for you, don't let anyone do that to you. Just move on and enjoy the car and then the next time your are in the market for a BMW, consider this incident in the future when you are choosing a dealer.
Not sure if that helps at all, hope it does, but probably doesn't