Am I just weak or is it okay to be sad about this?

I've been quite literally upset about this for a minute now.

I am in my first year of high school and I suck at it. I am well aware I suck at studying and that I am stupid. I don't mind it when grown-ups say it with a smile or if my friends tease my stupidity. Idc it makes me want to try harder, though that doesn't last very long until I get tired, so tired I lose motivation to do anything.

This one cram school I went to check out, we did a practice class (mathematics). The teacher was so sweet and lied to my face saying I was just fine, I only got a few questions right. But the boss came in, I said I did fine cuz I believed in what the teacher said. I rarely get told that so I was pretty happy. But then this man just went full out saying "oh no, she was just being nice, behind your back she said you are severely damaged and she is right, you are severely damaged. " He went on to say that multiple times, like,"if you go to the other one or choose not to do anything at all that's none of my business but you are severely damaged so I expect you to fail"

Like, sir, I am well aware of that. I did not come here to get scolded, I get that all the time at home, I am here to get help. And now I am just sad. It was pretty discouraging. I mean, I get that I am stupid, and he isn't wrong at all, but it just hurt.

Also what hurt more was when I got upset and told the incident to my dad and he was like, well, you just have to take in the truth.

Like, yes, I get the fact that it's the truth, I'm sad, let me feel better.

Idk, am I just weak? I mean I get that some people are just gonna go, yes, just study bitch and I don't blame you, and that is very true, you are very right, but, idk.