I went to a French course a few years ago, so I know the feeling. My advice would be the exact opposite, to participate as much as you can, that’s what will help you in the long run with the stutter but I know it may be scary at first and you’ll have to build up to that to liberate yourself of that fear (that we all share). At first, you could speak to your instructor/s and tell them that you have a stutter and if they could not pick you on the spot to speak and only if you raise your hand as that will build your confidence the more comfortable you are to answer the more frequent you will participate and get as much out of the course as possible. I hope this helps, wish you the best of luck.