Important issue for girls: keep a close eye on your iron levels, especially your ferritin level. (Pediatrician normally does not include ferritin test when ordering bloodwork.) Anemia in teenage girls is common; in teenage girls who run, it is very common. If there's a sports physician near you, go see him/her. Your pediatrician might say "your level looks normal", but that might only be true for an average person. Runners need more. Most studies show that a distance runner needs a ferritin level of at least 25, otherwise it will hamper performance.
I would have it tested now to see where you are, then again in three months (to see what effect your summer training had, if any.) It takes weeks to build it up, so you don't want to be in a position where it's October and you have low iron. You will get halfway through your 5K, and then you will just run out of energy, and you'll be scratching your head wondering why your training is not producing results.