I felt a very small lump on my testicle?

I'm 15 years old, and i felt a small lump, or as I would describe it, a very small pebble feeling thing on my left testicle, the rest is smooth, and it is definitely on the testicle. I'm not sure if because its so small that it is testicular cancer, and does this sound like anything else to any of you? Also, my uncle died of testicular cancer at the age of 20. Actually, I would describe it much smaller than a pebble size, maybe like a very grains of sand, the "lump" is very very small, on the bottom of my left testicle, and I am fairly certain that it is not my epididymis.