Calm down. You are never doing yourself a favor by panicking. I think you'll be fine.
This shouldn't jeopardize your graduation if it was contained and accidental (and not grossly negligent). What the privacy officer needs to know is all the details of what happened and that it won't happen again. Think about what you did and, if you did anything wrong, what you should have done (eg. how were the files secured? How should they have been secured?). At the meeting, be sincerely apologetic, accept responsibility for the accident, and don't make excuses. Make sure they know you are aware of HIPAA regulations and their importance, that you will make sure you will not violate regulation in the future, and that you'll be fully cooperative and compliant with however the hospital decides to resolve the matter.
Also, I'm going to suggest that you delete this thread, or at least your comments in it. This situation might get a lot more complicated for the officer/hospital, and potentially a lot worse for you, if its found to be described on a public forum. You have your answers, now protect yourself.