This is just a random Internet stranger's opinion so take it with a grain of salt, but I think one aspect that you should take into consideration is your need of friends and your dislike of sitting by yourself. You're already in 12th grade, making new friends in class right now is basically impossible since, as you said, everyone has their own clique. With your current personality I have no doubt you'll have an easier time making friends in fresh new settings, like college or something. So maybe work on being fine on your own and not needing anyone to sit with you at during lunch.

Also, while I don't think it's impossible for a (self-described) monotonous introvert to be outgoing and interesting and energetic, I don't think it's necessarily a good idea. That life is exhausting and if you "fake it till you make it" you'll probably give up along the way, or your introverted persona may occasionally slip through the cracks as you can't keep up, which would appear really jarring and pretty weird (speaking from personal experience on this).

All and all this is just that - a random stranger's opinion. I think you'll know what to do.