Throw in the NASA form within ten days from the event, that is what it is for. After that, accept the consequences of your mistake whatever it turns out to be. Under no circumstances lie about anything, and do not do the same thing again any time soon. Give a full and honest accounting of the event in the ASRS (NASA) form. I tend to doubt the FAA will pursue it because there was no safety incident involved. This student apparently had a first class medical anyway. There was no apparent risk to anyone's safety and it boils down to a compliance failure. I would not volunteer the facts to the FAA other than the ASRS form. The only reason I think you might see action on this is the school has established a pattern of compliance problems in the past. Also, get the AOPA legal plan for the next time around.