I went a few months ago and was shitting myself just like you but honestly it wasn't so bad, I actually wanted to stay longer after my two weeks.   Not sure where you're from but in the UK (if you get picked) you'll need to be sworn in so you'll have to say a few words in front of the judge, defendant, fellow jurors, and a few other people. Try not to worry about it, just remember they're all professionals and have seen others stutter so it really isn't a big deal.