Agree with previous posters -- great that you went in there not only with an apology, but with a way to benefit the entire program by presenting to those coming behind you so that they could learn from your mistake and prevent them from making the same type of error unknowingly.
These are the kinds of things that make you open your eyes and really be aware of what's going on around you. It's one thing for students to read about something like this in a textbook (which seems like a, "well, duh, I would never do that!" type of thing), and it's another to see that it can even happen to "one of them" in real, actual life.
Good job, and good luck!