Hi Cali Kate,
At 13, you are probably still cheering with girls who have barely started/haven't finished puberty yet. Itty bitty girls are just easier for flying purposes, but you might find that later on in high school things even out a bit more. I am 5'3.5" and I was a flyer in college. Some coaches like the look of taller flyers because our legs look pretty in stretches!
For now, I agree that you should take what position is offered to you, but if you are really passionate about flying you might consider upkeeping your skills with some all star flying classes or private coaching sessions. This way, you will be ready to fly if a position opens up later in high school or college.