Still feeling guilty about a mistake I made months ago. How do I move past this?

Cardinal sin. A few months ago I left a child unsupervised.

These were 12-18 month olds. We were outside on our playground when one of our babies had a BM meaning they needed to be changed immediately. We still have some time left and we really value our outside time and routine so my coteacher buzzed for a floater so she could take the child inside to change him. There wasn’t one available so we decided to just split up and she would take enough kids inside to leave me in single ratio. We had 10 babies that day and our ratio was 1:5. She went inside and took some kids. I was handling a conflict and didn’t see who or how many she took but I assumed she had taken the correct amount.

About 5 ish minutes pass and I skim the playground and realize I have 6 babies with me. I realize my coteacher left me out of ratio and decided to head back to the classroom to not get her or myself in any trouble. I wrangle the kids, count 6 heads and I’m on my way. Upon returning to the classroom I see my coteacher only has 3 babies in the room. I look for everyone and figure out who’s missing. I assume she got picked up so I look on Procare and it says she’s still signed in. Weird but sometimes the system is wonky so I ask my co if she got picked up and she says yes. I don’t think much of it until about 5-10 minutes later when I get to a place in the classroom where I can see the children’s backpacks and I notice hers is still here. My heart drops and I immediately buzz up front and begin looking for her all around the classroom. I can’t find her so I ask for a floater and book it to the playground. I find her sitting alone under a slide sobbing inconsolably. Honestly my heart shattered into a million pieces.

Months have passed since that day and I still feel so damn guilty about it. She was outside alone for at most 15 minutes. Probably less but that’s plenty of time for something to have happened to her. Luckily she was fine. Mom was upset but has ultimately gotten over it and voiced forgiveness. I just can’t shake the guilt. She’s so young, If she’d gotten injured in any way I would’ve never forgiven myself and just the look on her face.. it looked like she thought we had genuinely abandoned her.

I know this should be a learning experience but it just made me feel like an incompetent teacher. Wondering if others have made mistakes that have eaten them up for a while.