Your experience is very close to mine. Was sent to a private school with an entrance exam and brilliant at turning out Oxbridge and Russell Group candidates.
Then there was me. Appallingly mediocre A level grades, went to an ex Poly to do a law degree I Was not suited to. Was already struggling with my mental and physical health (had ME for some years by then, was battling what would later be diagnosed as CPTSD, OCD and BPD/EUPD. And severe PCOS. Spent my time at Uni either in hospital or just binge eating and getting hideously fat. I hadn't wanted to do the course but was terrified to tell my parents that I wasn't up to going to Uni. It's not that they pushed me into doing law, but they didn't like me doing the other things I was interested in and they wouldn't hear of me taking some time off richer my head together. Actually that's not fully true, they did allow me a year to come late my A levels. Due to health I had to take some of my A levels in autumn .
I did want to leave home , and knew I couldn't work full time, I didn't have much confidence in myself . I was far and no one would want me My dad would tell me. My father was abusive physically and mentally. I was bullied throughout primary school and a little bit in my first two years of secondary, sexually abused by a grandparent and two other people at different stages at my childhood.
I have a lot of shame that I wasted my life. Before ME, I was performing classical singing at a fairly high level for my age, performing quite advanced music for my age, told I should study at music college but I spaffed away my education. Got into serious debt twice.
I'm now in social housing in a poorish (but not bad) area. I now have support to live independently in my own home. Some of the psych drugs I was put on (before had a proper diagnosis) caused me issues with my movements and balance and I get tired v easily from the pain. My memory is not what it should be.
I feel guilty that my parents paid so much for my education but I feel nervous of apologising to them in case I release a ton of resentment. Which is kind of deserved but also I feel I didn't choose this way of life. But maybe I'm being a victim thinking like this ? I don't know.
Feels therapeutic writing this down. Sorry I've not been able to contribute anything more helpful OP. FWIW, it feels like your own issues aren't your fault and maybe it's trauma you went through causing you these feelings. I still am paralysed by some things my dad and those bullies told me and what they did, I understand self loathing and shame and inner critic very well. But I did not stand up to my dad when I should have , I did not have any self agency or much of a backbone and I do feel very silly about that. I wish I had just left my parents and had the courage to get a place and some decent therapy until I was ready to know who I was and what I wanted to do in life.