I myself am a pretty heavy stutterer. I'm still 23 and just got my first job this spring so I don't have nearly as much experience as you, but I hope this comment can help somewhat. So, I've felt a lot of what you felt. Being ashamed, having no self-esteem, being embarrassed, all of that. And I think the best thing to do right now is to talk about it. I know it's a difficult thing to do. But I think it'll take a lot of weight off your shoulders if you have a discussion about it with your manager, and maybe even with your other colleagues. You're worried that your "slip-up" might cost you your job, but in reality I'm certain that your manager couldn't care less that you have a bit of stuttering. I stutter during every sentence I say at my job, but my colleagues and team leader are very understanding. I did have a small talk about it with my manager, but he assured me that my stuttering wouldn't be a problem at all, and I've felt a lot more comfortable ever since. Many of my colleagues probably don't know much about stuttering, they only know that I talk weird, but they don't seem to care about it at all. They treat me just like any other guy. So, I hope the best for you! I'm certain your colleagues won't care at all that you have stuttering. I hope that you'll be able to feel relaxed enough that you don't care about letting some stuttering out.