The fear of missing out, more commonly known as "FOMO," is the most commonly experienced mild social stressor of our current lives. Whether it be concerts, parties, events, or even friends hanging out without you, missing out, for lack of a better phrase, always sucks. "Missing out" on things was a huge problem for me personally up until recently when I found a way to deal with things in a way that worked for me. However, this was not easy and took a lot of thinking and practice, which I could do a lot of especially during quarantine.
Naturally, a brief notice before I continue- the thought process described below is just something that helps me cope with feeling left out or like I'm missing out, so it might not make sense to everyone but that's okay. Moving on-
The key to getting over the more severe feeling of anxiety when missing out on things is having confidence in both yourself as well as your friends. Reassuring yourself that it is okay to not be everywhere all the time is reinforcement that this is a problem that is normal and that everyone deals with at some point. It is important to remember that there is most likely going to be another party or concert or game or dance which can be attended in the future, so missing one is not so bad at all. If it helps at all, turn off your phone for the night (because ignorance sometimes truly is bliss) and try and focus on whatever it is that occupies you at the moment. Although it sounds entirely over the top and overdramatic, sometimes it is easy to feel that after one missed event you'll be left behind socially for good. However, it is a shared sentiment that I've found many people to have in common. Here is where it is important to have confidence in your friends and the fact that they won't exclude you just after you missed some lame party. And if they do, think about if those are actually good friends or just people who like having fun with little regard to your own feelings. Personally, I don't have any friends who would abruptly or even gradually stop hanging out with me just because I missed something because good friends don't always need to see each other 24/7 to keep a healthy and close bond. So basically, have faith in yourself and your friends that even though now anxious feelings are running rampant, social status and friendships will still be secure. (I had a cute little phase over quarantine in which I managed to convince myself that the majority of my friends no longer wanted to remain friends with me. Don't judge because there was a lot of time by myself and time to overthink everything to the moon and back.)
What also helps me is thinking about my far future. For example, this weekend I have to miss my buddy's birthday party for a volleyball tournament I don't want to play in. I'm also missing a week-long trip to Georgia with a whole bunch of my friends for volleyball over the summer. There is nothing I can do about either situation, so I try to make the best of it and think about college, my career path ahead of me, and the life I'll be living in ten years. In ten years, no one will even remember who went or who didn't go to the birthday party (can't really say the same for the Georgia trip since that is notably more memorable, but I guess I can't win them all) and maybe the extracurricular activity of playing volleyball helped me (probably not) get into my dream school (hey, Vanderbilt). It might not always be true but thinking about the far future always helps me think about how whatever else I'm doing is bettering me rather than stripping me of a more beneficial experience. On the other hand, if the reason you miss out is because of a strict parent and not because there is a conflicting event, I myself have not mastered the art of seamlessly getting over it and moving on (and I deeply apologize because that is always beyond unpleasant). If this is the case, I recommend again turning off your phone (or at least not checking socials) and finding something productive to do.
Lastly, if missing out on things makes you feel insecure regarding the way others view you, just remember that the spotlight effect, which is the phenomenon that we believe our flaws and mistakes stand out to others far more than they actually do, is real and no one is going to think any less of you for either involuntarily or voluntarily missing out on something.