p. 225
नित्यं नियमेन अज्ञातचर्या गूढचर्या मे मम कर्तव्येति
In plain words
"Always, as a fixed observance, a conduct unknown to anyone — a hidden practice — is what I must keep": me here means mama, mine.
Close to the Sanskrit
"Always, by rule, an unknown conduct — a hidden conduct — of me, that is, mama, is to be performed" — thus.