I have social anxiety but my dream is to be a singer/songwriter. I recently quit my job because I felt self conscious and paranoid about people from my secondary school coming in and embarrassing me?

Don't feel bad about quitting this job due to your anxiety. It's good to focus on healing first so you can function again. Have you heard of Emotional Freedom Technique (EFT)? You can learn it for free online, and it's known to be highly effective for treating anxiety. I actually wanted to be a songwriter too at some point. The online songwriting course by Berklee College of Music was very helpful for me; there were peers who reviewed my songs without needing face to face interaction. If that's not yet comfortable for you, you can read 'Songwriting Without Boundaries' - the exercises there helped me get comfortable with rhythm & rhyme in the words. While you write your songs, having friends and supporters by your side will be very helpful. Don't try to convince anyone to like your music, but rather welcome the people who like it already. You can try performing with friends and in smaller crowds as you begin. I've also found it very enjoyable to jam with other songwriters in a small group.