Rock of Rancor glitch

I'm currently in the middle of the Rock of Rancor quest, where it is asking me to throw a fire sand stick at the rock. However, when I get there, the rock is not selectable (I'm on ps3). It's definitely the rock, as it's glowing and there are other people there doing the quest fine. Tried Restarting the game a couple of times to no avail.

You know what, I've figured it out, I had to go onto my inventory and use it. My apologies.