Did I do something bad

Things to consider regarding an error: time of the order change (not the time you actually saw it); time the first oral dose was given. If you gave the morning dose as IV, the next dose (oral) should be given at the new time (1750) for an increase in dosage. If the dose is decreased, the pharmacy won't release the med to begin until the next day.

If the order was changed before you gave the morning dose, then yes, there is the error. But the question is why did you not see order? If the orders were checked, the meds were pulled and given as ordered, this is not on you. The times assigned to the new med administration is a non-factor unless the order was written BEFORE you gave your dose. Even in that, we would notify the pharmacy for an adjustment of the start time for the new med to begin.

Nurses cannot be glued to computer screens and administering meds simultaneously. But a great practice to have is to give a quick final glance at the orders as soon as you start scanning the patient and the meds AT THE BEDSIDE to avoid such hiccups. 

Contrary to popular opinion, nurses are not psychic or mind readers (we do come close, sometimes??). We do not know when a provider will change any given order...unless he calls you in advance, which most of them do not. If you have a supportive instructor who's been in your current situation REGULARLY on med/surg units (because this is an extremely common occurrence when orders change), he or she should have explained this to you. 
 
If an error occurred, that's on the instructor. You're just the student. He or she should have been right there with you verifying the correct properties (rights). But overloading your patient with fluid by giving the IV dose? Absolutely not!! Chances are, the meds were changed in anticipation of discharge.