Short answer: The passage you're thinking of occurs at the beginning of §52. Here's Stambaugh's version:
The explication of everyday being-toward-death stayed with the idle talk of the they: one also dies sometime, but for the time being not yet. (p. 236)
Longer niceties: You're right to highlight the evasion in the "everyone." In §51, Heidegger address this more or less head on, where he deals with the similar idea: "One also dies at the end, but for now one is not involved."
The public interpretation of Da-sein says that "one dies" because in this way everybody can convince him/herself that in no case is it I myself, for this one is no one. (p. 234)
This mode of evasion he characterises as a "tranquillisation" (Beruhigung), a way of avoiding death even up to the end. However, while its important for Heidegger's initial characterisation of the everyday attitude towards death as a way of avoiding death, it's not the main evasion (and this will bring us closer to what to do with "I will die").
Returning to §52, Heidegger notes that:
In the "also sometime, but for the time being not yet," everydayness acknowledges something like a certainty of death. (p.236)
In short, just affirming "I will die" can simply be yet another way of avoiding taking death seriously. After all, this "I" needn't be me. It could be understood as just another appearance of the "one" (das Man), and so he adds:
They say that death is certain, and thus entrench in Da-sein the illusion that it is itself certain of its own death. (p.237)
It's also worth noting that "I will die" again sounds like it has a temporal displacement: "I will die, someday, but not yet". What's important is how this is held:
Thus the they covers over what is peculiar to die certainty of death, that it is possible in every moment. Together with the certainty of death goes the indefiniteness of its when. (p. 238)
What's at stake in this isn't just something in the imagination; it isn't even really about death per se; its something in one's attitude towards life itself. Authentic being-towards-death "brings [Dasein] face to face with the possibility to be itself" (p. 245). It's this encounter---with the possibility of being itself that ultimately characterises authentic being-towards-death.
