You probably are. But most of your colleagues as well :)
Most adults are kids in big meat suits, they fake it a lot.
I started to live like I was not completely worthless at 35.
Not saying that to be proud of it, just stating that if you think humanity should do better, the first person you'll judge is you.
It will be glaringly obvious you are not meeting your own standards.
The higher your standard, the longer it will take for you to reach them.
And the way to get there faster is to ignore the shame, and do it anyway. Because if you don't, your growth will be slower, and you will do more damage for longer.
Real life means real consequences.
It will make you more tolerant of others as well. Way more tolerant.
Don't worry, you're not a real imposter. You've just inadvertently ended up in a position where you're expected to be one. Just fake it until you actually become a true imposter.