I have a benign bone tumor in my knee? is this dangerous?

ok so i was in track and my knee started hurting really bad when i would run or jump or even walk for a long time. so i went to the doctor and they took xrays. apparently i have a tumor in my knee. the doctor says that it half a centimeter right now and its not really mejor. so i dont need surgery unless it get bigger. also i have to get xrays once a year to be watching it. but im not allowed to be in sports anymore and i am a really activem person. so no more running more thatn 2 laps or doing anything involving my legs to be active. the other day i went on a peddle boat and suddenly my knee started hurting really bad and so i had to stop peadling but then it stopped but it kept coming back but i kept pushin it and pushing.and im worried that if soon there is a possibility that my leg might get cut off. i mean im only 14 is this possible? so sorry if im overacting but i really want to know is this tumor bad?