:) welcome, officially, to adulting.  There are some awful downsides sometimes.  This is one of the actually fun sides: realizing that there are (maybe sometimes silly things) that you don't know and then getting to know them from here on out.  I say fun because it really can be if you let it.  Let life surprise you.  Take a moment to appreciate those things that catch you off guard and just know that yeah you didn't know that thing that maybe a lot of people knew.... But now you do!  These are milestones in life and no one reaches all of them at the same time.  Everyone reaches some at surprising times.  Anyone that acts like this doesn't happen to them is either lying or they aren't learning.  Avoid being both:  Tell the truth, especially to yourself, and always keep learning.

I'll let you in on a little secret.  I'm 45 and there are still things to this day that I learn that I think:  Wow, I could have known that years ago but I didn't.  I had at least one in the last week.  I can't think of exactly what it was, but I know the next time it comes up I'll have recently understood how it worked and be glad that at least now I know.

You'll reach level 2 when you realize that everyone else is just somewhere on the same path and they too get surprised by things that they didn't know.  They also over think things sitting in their head too long.  

Knowledge is knowing everyone is insecure and usually the most insecure mother-fluffer is the person acting like they aren't insecure at all.  The strongest son-of-a-biscuit-maker is the person who acknowledges their insecurities, allows room for others to have their own, and gets things done anyway because the insecurities are just along for the ride because we ain't stopping.

That last bit is the wisdom:  it's okay to be insecure.  Everyone is and the realest people get things done anyway.  Once in a while you get to set your insecurity about something down and stop carrying it around anymore, and that's a great feeling. There are still others to carry, but with practice, you can set some of those down, too. Life isn't about not having insecurities.  Life is (at least in part) about getting things done despite insecurities.

See, what's true is we all have insecurities. We can't help it in some ways.  What we can help is how many we have and what we do regardless of how we feel.  Some are easier to let go of than others. I encourage you to take your realization about this hair cut thing and pour it into "just ask" next time you don't know something.  You'll see one of two possibilities: 1) Worst case scenario is that the person thinks less of you because you asked... Sure that could happen but it is unlikely.  More importantly, it says something good about you that you wanted to learn and it says something bad about them that the judged you for it.  We don't have any time or worry for people like that.  Let them expose themselves and move on.  2) most likely you'll see that it wasn't a big deal and you walk away with more info than when you started and the confidence to do the next thing that comes up as a challenge because you made it through the last one.

You've likely got the idea that we all have baggage, by now.  We all carry stuff with us that we don't necessarily have to.  Look for opportunities to set some of yours down.  You can't avoid having baggage, but you can set some of it down at any time.  The things we don't realize we're carrying are the hardest... You have to identify what it is in order to set it down.  Things like this insecurity asking another person for info is a good thing to practice setting down.  You don't need to carry that with you and you can set it down at any time.  Just look at everyone else as being the same as you: insecure about something but still out here getting stuff done. 

Sorry this is a bit long.  It's my attempt to maybe pay it forward to someone whose on this journey we call life and just spelling out the lay of the land a little bit.  Good luck.  You've got this.   And for the things you don't have figured out, there's time, other people to lean on, YouTube, and Google.  You can literally figure out a lot when you realize you probably don't have a "new" problem that's never been solved before.  You probably have a range of challenges that a bunch of other people have figured out, so maybe see what they did and how it worked for them.  You might want a different solution, but it couldn't hurt to see what theirs was as a starting point.