Am I a goldfish trying to climb a tree?

Is it too far fetched?
"Everybody is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid." - Albert Einstein

I don't know. People around me think I'm stupid, and that I won't even be able to finish year 12 this year. In knowing this, I'm starting to doubt myself too!

I remember when I was young I had ALWAYS wanted to be a lawyer, and that I want to be a Harvard Law School graduate.
Now is the time to start preparing to apply to universities, and I know of many of my friends who are applying to Harvard, Yale, Princeton, Oxford, Cambridge, etc.
Just these recent years I'd already started doubting myself.
When someone ask what I want to do, I'd say "Law.... but I know it'd be difficult to get into."
it's like I have no self-esteem, like I don't even believe that I am capable to get into Law.
Maybe it's the OCD- all this worrying. It's really frustrating, I just want to be normal again. I have enough to deal with and I hate everything.

Anyway seeing some of my friends apply to those top universities, I want to be able to get into Harvard too. That's been my dream since I was little. I have the chance to apply, why not now that I'm right in front of it.

I asked my dad his opinion on me applying to Harvard and he sort of raised his tone.
He lectured me on how when I was 14, I moved to Surabaya, to live on my own, and then only after a semester I didn't want to go there anymore. So I am fickle. And if he had paid the expensive enrollment and everything to go to a top university and then only after a semester I change my mind, he'll have no more money.
And then he said- but then you don't even know if you're going to be accepted or not.
(I felt as if he was implying that I'm not capable enough to get accepted- and this made me sort of doubt myself too- am I a goldfish trying to climb a tree? I am definitely not the smartest person in my high school there are way more people who are better than me at everything in my school, but I've always been ambitious.)
Do I walk away from my childhood dreams because people doubt me? I've always said that you have to think big to be big and great, you are what you believe, but now I'm starting to doubt myself too.