how can i stand up for myself?

anxity sucks so much and I know from personal experience how much it can limit what you cant and can do which is a bummer. they way that I got rid of my social anxiety (sort of.. its still there but its not as bad) is that I told myself that I wont stop myself from doing the things that I want to do and somehow that has helped me.. but the thing is you actually have to stop overthinking.. most of social anxiety is due to fear of being judged for our opinions, but the thing is we will be judged whether we say something or stay quite so we might as well just got for it and don't give a fuck about peoples opinion and do whatever we want ( as long as its safe)

In addition to what Valentina suggested I'd also encourage you to engage in positive self talk. While I don't have severe anxiety in most senses I still do have difficulty with public speaking. So whenever I have to do the whole time I have positive thoughts running through my head.
"You've got this." "You can do it." "You're confident." "You know your shit."
It may seem silly, and I still get nervous, but it works. You would not believe how often I get commended on my public speaking skills. I'll be shaking after because it's still stressful but it has gotten easier, especially knowing that no one can tell that I'm nervous.