The adults who seem to have it all figured out are mostly googling stuff at midnight, same as you.

Competence from the outside looks like knowledge. From the inside it is mostly a willingness to look things up and keep moving while unsure. People who appear settled have simply had more practice being uncertain without treating it as an emergency. Nobody graduates into a state of knowing; they get more comfortable operating without the answer in hand.

When you catch yourself assuming everyone else was issued a manual, ask one of them what they were unsure about at your age. The answers tend to be reassuring. Then go and look up whatever you needed, and stop counting that as cheating.