This is a hard lesson, but it sounds like you are an honest, caring, nurse who deserves the good luck you are having with this situation. You will get over this, and come out on the other side a better nurse for learning this very critical lesson. You can count your blessings that your patient was not injured and that you are being given the opportunity to do better in the furture.(Good job to the charge nurse and DON). I can say this from first hand experience having made a med error in my first year of nursing too. No matter what type of error we make as nurses, because we care, it will be a life altering experience. I think that is the part of the job we have to struggle with, so keep on caring, just remember to care for yourself too.
Good luck, and keep on caring.