Are the examiners aware of your stutter? It's their job to accurately assess your work/answers. If they fail to take your stutter into account then they suck at their job. Send a few emails to the examiners (or whoever is in charge) saying you're worried your stutter might negatively affect your results. Also, right before your exam, explain to your examiner in person what your stutter entails and what it sounds like so they can recognize it. You're not on a level playing field with those that don't stutter. The examiners need to be aware and adapt.