Final answer:
The nurse should immediately call the patient's physician, report the medication error, document the actual amount given, follow any instructions, and monitor the patient.
Step-by-step explanation:
When a nurse realizes that more medication was given than was ordered, the correct action to take is to call the patient's physician and report the error. This is in line with the principles of patient safety and ethical nursing practice. After informing the physician, the nurse should also document the actual dose given as well as any subsequent instructions or interventions that are required due to the error in the medical record. This documentation is crucial as it maintains an accurate record of patient care and can be important in monitoring the patient's response to the overdose. Additionally, the nurse should closely monitor the patient for any signs of adverse effects as a result of the medication error.