Was I really a “mistake?”

You’re not a mistake.
You’re just different. different than most common & ‘normal’ people defined by standard society’s expectations.
Hell, you might have some potentials that’s WAY above the ‘average normal’ people. Like a peacock with its most beautiful feathers, if used & utilized well.

It’s always a no-secret that ‘different’ people like us are always seems to be feeling lonely (even terribly lonely at times!), depressed, misunderstood, and outcast.
Even Nietzsche acknowledged this very well and he once said: “The individual has always had to struggle to keep from being overwhelmed by the tribe. If you try it, you will be LONELY often, and sometimes frightened. But NO price is too high to pay for the privilege of owning yourself.”

Oscar Wilde’s famous quotations:
“Most people are other people. Their thoughts are someone elses opinions, their lives a mimicry, their passions a quotation”

And I sincerely hope that you can be encouraged by further quotes from popular figures, to give you Hope, to know that you’re definitely not all alone, and that you might have some great potentials waiting to be unleashed hidden inside of you:

“Here’s to the crazy ones, the misfits, the rebels, the troublemakers, the round pegs in the square holes, the ones who see things differently — they’re not fond of rules. You can quote them, disagree with them, glorify or vilify them, but the only thing you can’t do is ignore them because they change things. they push the human race forward, and while some may see them as the crazy ones, we see genius, because the ones who are crazy enough to think that they can change the world, are the ones who do.” – Steve jobs

“History shows us that the people who end up changing the world — the great political, social, scientific, technological, artistic, even sports revolutionaries — are always nuts, until they are right, and then they are geniuses.” – John Eliot