Yeah, in those situations when they repeat my order incorrectly, I pretend like I'm not sure about it so I can repeat it without acting like it was their fault. For example: Cashier: "Milk and Sugar, right?" Me: "Uuhhhh... actually can you do it without sssssuuuu--" Cashier: "No sugar?" Me: "Yeah!" Cashier: "Okay, so iced coffee JUST milk?" Me: "Yep!" Adding an "Uh" or "Um" at the beginning makes it easier for me to start the sentence since I have to slow down my pace and makes it easier for me to say the rest even though I'm in a stressed situation. And even if I do stutter, the cashier usually finishes the sentence for me, as seen in my example.