I wanted to explore my own world without any interactions with levels, pressure plates, etc. So I put a command block that makes me put in adventure mode when I step on it.

I de-opped myself and I stepped on the command block. I realized that I can't re-op myself since you can't customize permissions while on adventure mode.

I exited my world, then I tried to fix the issue. Turns out that you can't customize permissions outside of the world.