When i was your age meeting the parents was always one of my biggest fears, but its something you have to do, having a stutter never stopped me from pursuing women! Hell i would have to call the house line to speak with my girlfriend at the time, super stressful. What would help me is taking a half hour or so before hand and just focus on my breathing and really get myself in a sort of zen state of mind. You could focus on anything just try not to think about the situation during your breathing. I would also suggest bring something small to grease the palms of the parents, this never hurts. One thing that you should remember is that if you girlfriend is comfortable with your stutter then she has probably brought it up to her parents as a heads up. Most parents although scary are really nice people. good luck!