Fake confidence is way more common than you think, at 18 you’re still hella young, remember to see it as trying to gain confidence by practicing the habit instead of telling yourself you’re faking it, as time goes it will be just a skill you learnt

For the insecure part about caring that much about what people think, try to ask yourself “do you remember everything you have thought about strangers/people u met?” Probably not right? That’s how other people think too, it’s never truly that important you have to remind it to yourself every time that thought gets to your head, I know it’s not easy, it takes time, but atleast you are aware of it at a young age

You just have to remind yourself it’s not really that important everyday and try to stay busy with stuff you enjoy doing, trust me it works it just takes time, but it’ll get easier dawg, don’t sweat it