I thought the idea would be explored more.
It was a great idea, but I feel you could have explored it more, or done so with a bit more flair.
Your comments kinda gave the entire story away - I was hoping to see the possibilities of a real-world undo explored. Maybe time travelling, maybe he'd go back to yesterday and jokes would ensue... I can't think of many cool ideas off the top of my head, but I'm sure you could if you sat and had a long think about it.
I can see you were going for a quick punchline, but the comments and the slow narration and spinning keyboard made me think it'd be a longer story, leaving me disappointed.
The graphics were okay. You could have drawn in the mum/dad. I wasn't sure who was talking - in the first fram, I first thought someone inside the box was talking.
When things disappear, you could have had them tween out - maybe reducing their alpha value. That would kinda make the events more visual.
The audio was all pretty clear and the idea was cool, though.