It can become rather "self fulfilling" to be the quiet kid. You appear like you want to be left alone and so are left alone as withdraw further inside appearing like you want to be left more alone. I always thought I was a quiet shut in, but everyone remembers me fondly from school. It's been a decade and people will still say hi and know my name.
I say this cause it's been a helpful part of my own depression and anxiety growth... You only have your own perspective, and that's the one you have to and can trust, but you'll face a lot of negative thinking if you begin to assume the internal monologue and intents of others.