Don't lie to yourself. That's genuinely the worst thing you can do.
I used to consider myself short, and I still do. But I am 5'9. That's 2 inches away from the Greek average, and my mom is 4'11. Like even if i stay at 5'9, I will be happy, because that's still a great height.
Same for my penis size. It was quite small like a year ago - in comparison to the AGA, - and now it's 3.5 cm larger than the Adult Greek average. And I'm still in development. Like I feel hope, in myself, for developing better. And I try to get my best out of my development "time". I get a good protein and vitamin income and I exercise in.. multiple ways. ( ͡° ͜ʖ ͡°)
To be completely honest, I feel that all the time. You're not alone. Everyone has a fat belly when they sit down, unless they're fuckin slender man or sth. If you feel like that, and you're reasonably not fat, try exercise. I prefer martial arts, such as Tae-Kwon-Do, which help you work on every part of your body.
Also you're not dumb. It's just that people feel that somedays when they make bad decisions. To fight that thought, you must think of every right decision you've made. And don't tell me you've made no good decision. That's like telling me you've never seen a human being ever in yo life bro.
Even if you are "making bad decisions" at the moment, if you can change them, go ahead. Accept who you are and embrace it. The faster you do it, the faster your depression will go away. And if you want to improve yourself, set a goal and accomplish it. Because if you get that motivation from yourself, it's genuinely unstoppable.