I feel like I’m here by mistake

So I’m 32f and I’m turning 33 in a few days. I just can’t help but think that my life was a mistake. Although my parents desperately wanted a daughter (I have four brothers and I’m the only girl), it just feels like I’m not meant to be here. I have no friends, I can’t seem to get a job, I wasn’t the smartest kid in my classes in fact I was the slowest and had to get extra support in school. I was also the fat kid and I was bullied heavy for it by family and school kids. I have been anxious and depressed my whole life and people tell me it gets better but it never does. I can’t seem to have a healthy stable relationship with family or potential friends. My brothers are all successful and have their lives together so why can’t I be like them? I just feel like I don’t belong here and that they would all be better off without me (to be honest I’m not that close with any of my brothers). My birthday is coming up and I can’t help but hope that it’ll be my last and I’ll eventually gather the courage to let go and die. I feel that it would be for the better.