She won't necessarily say anything - i've not known many particularly caring teenage girls. If you're that worried maybe speak to her but i wouldn't advise it, the whole thing could blow up. Wait and see what happens, i shouldn't think your gym teacher would just call your parents without speaking to you first - they're there to pass on accurate information, not cause problems. If they do ask you anything you can just mention it's an old sporting injury or something - you won't need to show them and they have no right to ask to see anything either.

Try not to worry, this may well be a storm in a tea cup.