So I know that I very rarely post around here and tbh it probably isn't really any of my business anyway, but I just gotta hop on my soapbox for a sec and say that there really isn't any need to be that hard on yourself. Your art may need improving but at the end of the day, everybody has more that they can learn. Also, I know you probably don't want to hear this from me but you are only 13 - and though it probably doesn't feel like it to you, that's still pretty young and it's very likely that you and your art are going to grow and change a lot in the coming years.
To be completely frank with you, most people that I have ever seen just don't draw that well even through their early/mid-teen years. I didn't, my friends didn't... and yeah, that's totally normal. You just haven't really been able to put the time in yet. Comparing yourself to other people and saying "boy, they're so much better than me... my art must be crap" really isn't fair if you're 13 and they're, say... 27.
I don't know if it would make you feel better but if you don't believe me, I actually have
one of my first TLK pictures that I drew back when I was 13. I spent quite a bit of time coloring it and working on it and was quite proud of it at the time.
Compare to
one I did just now in about 20 minutes (with way less effort, if I'm honest).
It hasn't even been five whole years yet, and if I'm completely honest with you then I would say that writing is more of my strong point compared to drawing, anyway. But there's still definitely been a change over the years. A lot of it just comes with practice, though of course it helps if it's focused practice. I spent time watching speedpaints and tutorials on Youtube, looking at tutorials on dA, and of course making close friends who were really into art (which helped a lot).
If you focus and draw a lot with the intent of getting better, you will improve. I almost gave up with art multiple times because I felt like it was crap, but eventually I came to realize that I wasn't really being fair or realistic in terms of my skill level. A lot of it just comes with age and experience, so be patient with yourself.
Also (just as one last note) a quick look through your gallery made me think that you're probably using MS Paint, which... I don't know. I used it at 13 because I didn't know there was anything else out there, but it's definitely one of the most limited art programs I've ever used. You can find better free ones online - I'd start maybe with GIMP or Krita but there are definitely others. I'd also highly recommend Paint Tool SAI if you can get your hands on it. It's very intuitive and good quality and also affordable
though I got mine for free because someone gave me the file whoops. So that might also help you just to be honest.
Hope that helps or something, I dunno. I just wanted to say that. Good luck.