Sorry about the bad day, sweetie. I think you're just fine at work, though. Like someone else recommended, just tell the story fully the way you did here for us, and they're going to understand reason. Frankly, I think the likelihood of your even being written up is low. That woman from the other store was an impatient hot-head, and you maintained your cool amazingly well. Sounds like your colleagues and the manager on duty will back you, too, if there's any question at all.

Hope your little boy is feeling better soon from his cut finger. And I hope today and this next week go better for your both!