From my experience the more you try to not stutter, the more you do. Just try not to think about it and let it go. If the catastrophe happens, say sorry to the class and tell them that you stutter, if you can do that. My stutter has become much worse lately and if I would try to do some initiative speech from myself, even a short one, for ex. to explain why I stutter, I won't be able to say a single word in like 20 sec.