Social anxiety, FOMO, unhappiness

I’ve always struggled with social anxiety but I thought I had overcame it since it’s much easier for me to talk to people. However, I’ve noticed I still panic when I’m in a group of people, and I always assume people don’t really like me or care for me. And the biggest one is FOMO (fear of missing out). Tonight, ten of my coworkers went out for margaritas. I wasn’t even working today but someone messaged me asking me to come. I said I was busy and I was. But when I saw their photo uploaded later on, I just felt like crap. I felt left out. Even though I was invited, just because of the fact I “missed out”. I am always feeling like I am “missing out” and it sucks. IDK why I can’t just be content and happy with myself and my social life.