I'd actually slow down and work on the fundamentals more. You may be fast now, but you also have to think about what you are doing in order to improve. Once you've gotten the hang of those fundamentals, you can increase your speed without loss of quality, since it would become natural to you.

Looking at your gallery, I got to say, you have some great potential, especially for a 13 year old. If you seriously started studying now, you could have some amazing art, if not professional quality, by the time you're 18 or 19 (it doesn't take that long to improve if you do it correctly, actually). If you wanted to have a career in art anyway.