It's me. Me.
p 114 I find it interesting that the author repeats that word twice, "me". He mentions above that he is a killer just not of mammals, which is in itself intriguing (he finds himself unsure and scared when he has to kill a mammal but not when he kills insects or reptiles(the snake). One would think that it is because the goat in its size and amount of blood and organs and organism as a whole is way closer to a human than mosquitoes for example but then the narrator also mentions fights between people where death is highly likely and the ones beating up others are ready to kill. They become murderers the moment they attacked with no regard of how much they hurt the other person. As we know, the narrator has been in fights before (if he is the same narrator as in "House of Hunger" where he fought Harry, for example). Therefore, just as he claims that life is meaningless, so is his reluctance and his claims that he is not a killer, not a "man" in the sense that he is capable of taking a life.) Here, he emphasizes the difference between himself and soldiers and querrillas. He lists them just before these two sentences and then makes the claim that he is not them, he is not a part of war, he is no way obliged to, nor inclined to murder in the name of any cause. The simple sentence "It's me." he wants his sister to think about it from his perspective, summon all her memories and knowledge and find him indeed incapable of murder. The repetition is what turns his argument into a plea. he is begging her to please understand him. He is sincerely scared even if he points out himself that his reservations are illogical. This repetition in the midst of all his thoughts is what brings the readers back to the scene of his sister and him conversing. That is where his feelings come through even if what we read are his thoughts and words.