There you go again.
St. Peter does NOT warn about people privately interpreting the scripture!
Read the verse again until you understand it.
"And account the longsuffering of our Lord, salvation; as also our most dear brother Paul, according to the wisdom given him, hath written to you: As also in all his epistles, speaking in them of these things; in which are certain things hard to be understood, which the unlearned and unstable wrest, as they do also the other scriptures, to their own destruction." 2 Peter 3:15-16