I found it very interesting. I'm glad you were able to think about everything and finally got your voice to work. It's almost like a bad dream where you're trying to yell but you can't. This strange physiological reaction has happened to me as well. Anyway, sounds like it turned out well and I see nothing wrong with anything you did. I'm sure afterwards everyone realized how dangerous the situation had been and I'm sure none of you will ever make that mistake again!
It's completely possible to forget to shut the door fully and lock it so I can see this happening to anyone. It will certainly make me check even more than I already do that the doors are locked. I actually had to go check after reading this.