I haven't really considered confidence as positively or negatively impacting my speech until joining this sub, generally I attributed it to nerves. If I was nervous or anxious I would stutter more. Sure, that's part of it for me, but definitely not all of it. All this to say - Go in to your interview confident in your skills and the fact you got that far. Maybe consider not telling HR. People will figure it out. It could also be that saying something is almost setting yourself up. My interview went pretty well. I've got a pretty good job. You'll get one too.