Tampons and sports and one other question :)?

so i started my period sunday its only my second period so its very irregular and i have no idea how many days it will be. however, my sister and mother both have their periods for like 7-8 days so i think im going to have a very long one. i tumble (back handsprings/ back flips/ front flops fyi)/am on trampoline team ( routines on that really bouncey in ground trampoline. this class is on thursday and im wondering if i will leak by using a light tampon, because if i do straddle jumps on the trampoline it i leak at all it could go onto the white trampoline! how embarrassing, and to make matters worse, my coach is a guy D': so should i wear a regular sized tampon instead of a light? my flow is light tho :/. ok and last thing, whenever i change my tampon ( every 2-3.5 hours) only half the tampon is bloody the other half is still clean, why is this? im 13 btw and thanks for reading i really appreciate it <3