Please go easy on yourself. (And no more negative self talk!) It was a mistake. If any nurse tells you they have never made one, that would just not be true! You were outside your usual setting, I can bet things were busy. We are always time-pressured. I'm not providing excuses, but calling out possible contributing factors. If your manager doesn't assign you there again because of this, that is not a good way to react. You learned. There was no patient harm. Now you will treat all preop patients as NPO until you can confirm otherwise. You learn and move forward. Your entire career will go this way. Take care of yourself. I'm sure you are a wonderful nurse.