I'm sorry you're going through all this. Please be gentle with yourself. School nursing this year has been turned upside down. The expectations placed on us have been overwhelming along with the regular duties of the job. I agree that you should probably find someone to talk to about these upheavals. In my state, the teacher's union (which I'm part of) has a hotline for those needing some assistance, mental health, burnout, stress, anxiety, or otherwise. Hopefully your state does too.
The feeling of paranoia is hard to shake after an error, but again, please be gentle with yourself. I am certain that you have taken that error and it has made you a stronger, more diligent nurse than you realize. We're human.