Not you.
You are perfection my nonprofit unicorns.
But let's talk about making mistakes.
They happen when we are moving fast, juggling too much and ready to push send. They happen when priorities change, external stakeholders call the shots or the intern takes control. They do happen from time to time and, as the saying goes, the journey is the destination. In my view you have to explore some dead ends along the way.
Here's what I recommend (also possible responses in interview situations)
1- Breathe. The world didn't end because you put the wrong start time for the event in an email. Birds keep flying and grass keeps growing. It may seem like the end of the world to you, or someone standing over your shoulder, but really, is it?
2- Assess. What was the mistake? Was it an error (data, grammar, punctuation, spelling, etc.)? Was it an omission? What exactly happened?
3- Plan and Execute Your Response
First off own your mistake. Then figure out what needs to be done. Do you need to send a correction, retraction or some additional message? Who needs to send it? to whom? by when? Map this out and get feedback. Once you've figured out your plan, execute. In most cases, time is important and you'll want to respond as soon as you can.
4- Review Take a few deep breathes again and review what happened to get you into this pickle. What could change? If you could do it over, would you have been able to prevent it?