、。
However, the protagonist is aware of his own mistake.
Literal
However, protagonist [topic-は] self [of-の] mistake [to-に] is-noticing-[resulting-state-ている].
Literary-narrative register. 自ら is a somewhat formal reflexive pronoun ('oneself'), more written than 自分. 気づく = 'to notice, realize, become aware of'; on a change-of-state verb, ~ている marks the resulting state ('is in a state of having realized' = 'is aware'). 誤り is formal/literary; the casual equivalent is 間違い.