That's called a reality check, and it's a pretty common for lucid dreaming. The one I went with was placing my fingertips over my nostrils and breathing in through my nose. If you can breathe, you're dreaming. Picked that one because it's inconspicuous, just looks like you're scratching your nose. But the idea is to get into a habit of it so frequently that it's unconscious, and something your dream self will do. If you do it in a dream, you become aware because you're so conditioned to it, and you're able to start lucid dreaming. Works pretty well.

Also, good on you for being so aware of what you needed to do! I don't know if most kids would have come up with that, and that's super clever and mature.