Well, you apologize to them, get them the correct stuff, give them their copay back as well as waiving their new copay, then go on and find out why it happened, and file a report documenting everything you did and did not do.
Also, if they took some of the medication, call the physician let them know as well in case they would like to do something.
Good luck in your interview, I graduated from Iowa in 05, I really enjoyed going there, but remember to have fun, Iowa City makes it easy to do that 🙂