I’ll go first: “You have to have children when you’re young,” told to me when I was in my late 20s, with no desire to ever have kids, and no means to support them, by someone divorced multiple times with at least one adult child who does not speak to them.
Also: Responding to “How do I deal with this problem?” questions with “Oh, don’t worry about it, it’s enough that you’re even thinking about it!”
I’m 33 now, I don’t remember my sleepovers and all of my highschool friends are gone. We see each other every now and then when it’s convenient, but the new friends I made late 20s are the people closest to who I am now.
You aren’t “missing out” and feeling like you are is only going to make your confidence issues worse. High school is not what defines who you are.
You have the power to feel confident by altering your estimate of pleasing people. Please yourself, confidence and everything else you feel you want will come much easier. Good luck!