Will anything concrete change in your life --- will you get kicked out of your home, will you suddenly be financially responsible for things you previously weren't, etc.?
If it's any consolation, a lot of us don't feel like adults, and that's ok! My kids seem to think I'm a grown up, so I managed to fool them at least.
Just keep learning as you go, and ask questions. We all love talking about things we know/have experience with (just ask the average Lemmy user what Linux distro you should install...), and there's basically no such thing as "cheating" when it comes to figuring out how to be an adult.
One day at a time!
I have heard, but have trouble finding references to it, that you can build a simple arbitrary waveform generator circuit by using an analog scope, a photodiode, and a cardboard cutout.
You make a photodiode circuit that rails high with no light, but light on the photodiode pushes the signal low. Then you aim this at the phosphor screen with a cardboard cutout of the desired waveform: signal goes up until the phosphor trace is above the screen, and then it gets pushed low (i.e., feedback keeps the trace right on the edge of the cardboard).
Never seen it in action, but I choose to believe it works beautifully :)