OP, how old are you?
I thought I'd feel like you do when I graduated. I was also a straight-A student, top of my class, sailed into Oxford. Then it all went tits-up, and there were plenty of extenuating circumstances but I barely realised I could even reach out for help. Ended up scraping a 2:2 partly in due to focusing on other things (which became my career).
I said to myself, I have unfinished business with academia and one day I'll come back and rectify that. Guess what... within a year of graduating I couldn't have cared less.
Firstly, no one cares about your degree class in the adult world, any more than they care about my As at A-level and GCSE. No one asks, no one knows, it's never hindered my career.
Secondly, there are so many people in a similar boat. Some of the smartest people I know fucked up their education at some point and don't have the qualifications their intelligence might merit. You might not have applied for extenuating circumstances but you know they existed - be kind to yourself but don't dwell on it.
Thirdly, your degree class was never going to be the ultimate proof of your academic ability or intelligence. This ties together my first two points. Regardless of what degrees people get, they have to continue demonstrating their smartness to progress in the adult world. That's how I know a friend of mine is incredibly smart (and has a top media job) despite dropping out of uni completely. Or why I take another friend who flunked their A-levels much more seriously than some others in their field with Oxbridge firsts. It's also how I built a career I'm proud of. The ability to quickly grasp concepts, to make links, to articulate them well - all the reasons I was a straight-A student are all the reasons my career has been successful. I didn't lose my intelligence by crashing and burning at uni - that was just a low period in my life that ended up being a very small part of it.