Unable to blow up TNT

[butterbumps]

Hi. I just started playing Penumbra: Overture and I'm stuck at a part relatively early in the game. I have to blow up a part of the cave that has collapsed using a TNT barrel. The TNT barrel is in place, but I have no way of blowing it up. I looked up a walkthrough and it said I need to get string from the room that had the 2nd save game checkpoint thing (idk what to call those). However, there is no string. There is a box, and when I right click it says it's a box of string, but I am totally unable to pick up any of the string inside.