Let them know you might stutter in this interview. It might also help you relax. Also try and get your heart rate down whilst waiting to go in, work on your breathing, use deep and slow breaths. Most importantly take your time when speaking, dont rush yourself. If your having trouble on the word, stop exhale all residual breath and inhale, try and say the word on the top of your inhale, this helps me sometimes. Hope you get the job and dont stress if you don't. All the best.