I don't envy you. Being 16 is hard. The good news is that as you get older, you learn more about yourself and other people. The more you learn about the world and yourself, the happier you generally are.

A few things I noticed:

My memory is a total mess.

I find that when I have a hard time remembering things it's because I'm not really present in the moment, and I'm not really present in the moment because I'm not engaged in what I'm doing.

It sounds like you don't really have anything in your day that you can look forward to learning. That sounds very normal for high school. Your task is to learn stuff you have no interest in learning. Maybe spend some time thinking about your classes and look for something that peaks your interest. At that point, maybe put a little effort into learning about that subject. When I was in high school, I was naturally good at math, and looking back, I wished I would have put effort into going above and beyond my classes to learn about it.

working in the videogame industry

You don't have to live in certain spot to start working in the industry. Start a blog reviewing games or finding glitches in games if it interests you that much.

I barely talk

It's totally normal to feel awkward talking to people. Some people have an easier time than others, but it's totally normal to not find striking up a conversation easy. Unfortunately, it's pretty important to talk with people and interact with people. When I realized I had a hard time talking to people, I read How to win friends and influence people. If you spend a good 6 months trying to learn how to make friends and talk to strangers you should be in a pretty good spot. You'll also be setting yourself up to make new friends when you go to university.

So remember, being 16 sucks. No doubt about it, but the silver lining is that you're in a prime position to improve your situation.