Yours is a very common take on Rand's stuff. I don't think you're wrong about capitalism. It's a tool, neither good nor bad, but what people make it.

There's a book you should read. "The Sea Wolf" by Jack London. It is an excellent contrast of philosophies, one based on aggressive selfishness, another based on idealizing selflessness. Jack London is also 100x the writer Ayn Rand could dream of being.

Humans are not simply selfish. That would be a model for a lone predator, like a tiger. Humans aren't that self sufficient. Humans are, by necessity, co-dependant, even more than wolves. A lone human is very soon, a dead human.

We are cooperative and this is what Rand misses. Capitalism requires trust. Trust requires cooperation and rules. Rules require sometimes not pressing your advantage and showing restraint. Rules are not synonymous with communism.

I read this book when I was a teen as well. It has always struck me as shallow thinking passing as profound truths for people who had not thought about this stuff before.