Minecraft skin and model won't change(?)sentiment_dissatisfied

I recently just made my first skin because of some black bars appearing on my old skin. I thought it had something to do with the skin files however, when I uploaded my new skin, the black bars were still there. After a little bit of researching, apparently my player model is still on the classic thicc boi steve and not the slim Alex model. I tried changing it on the client and that did not work. I then tried to change it on the Mojang website and that still did not work. If anyone could shed some light on what is happening and how to fix it, I would greatly appreciate it. You can check my skin files on this site and see for yourself, if you are getting any errors.

I also made sure I am playing on the most up to date Minecraft version, the 1.15.2.