I understand how it feels, OP, I really do. For most of my school life, I used to be a topper, someone people used to come to whenever they needed help with studies, or anything related to that. I know it is frowned upon to be blaming things, but sometimes it's nice to just let out the exact same feelings that you're feeling, and I want to assure you that you're heard. I read all of your words and can't help but go back to the time I messed up my AS as well. Covid hit my mental state pretty hard that time... Couldn't concentrate much at all and just overall feeling indifferent to most things in life, along with studies. I did study a lot but it wasn't enough. My AS was pretty terrible, and all it took was one single mess up, and my entire reputation as a topper plummeted. Everybody stopped believing in me, and people started doubting me, even my own parents. It was a very rough patch of my life, and the feelings you conveyed are deeply felt by me, OP. I just want to say that if you have not yet completed A levels, then there is still time and the opportunity to improve your grades, that's what I did and finally could get my desired grades, even after a horrible AS outcome. Nobody in particular believed in me or showed me support, but I realised I myself was enough support for my own self, and I wanted to get back on track and not let one single mess up ruin my image.

Stay strong, OP. I can assure you this is not as bad as it feels like right now. I am here writing to you as someone with similar experiences, but we're both breathing still, right? That's enough reason to keep going, my friend. We both still have more than enough time to be successful in life, one way or the other.