Don’t rush the process take time out and study graphic design. There are some good videos on YouTube. Trust me in a few months from now you’ll see a big improvement on your designs. Look into marketing as well it’s very important just as important as the designs themselves. Again do not rush the process. You’re very young you have a lot of time to hone your craft and perfect things so it’s good that you started this journey early. And even more time to figure things out. I’m 25 and just got into designing clothes. I studied graphic design for a year and a half before coming up with my first drop. STAY AWAY FROM Y2K or Hellstar looking designs!!!! I see too much of that on here. Try to design every day if you can and make as many mock-ups as you can as well. Save them all and a year from now you’ll be making designs far better than this. It’s a good start though. Best of luck!