....what sins did Jesus fail to pay the penalty for on his Cross?
"All have sinned," is the very reason Jesus negated the rules against us as He bore the penalty we should have gotten for being a sinner from birth. That penalty on the Cross was not the Lake of Fire. Jesus did not go to the Lake of Fire while bearing our sins.
That penalty? Was being forsaken by God. Forsaken while our sins were being poured on His body. Not the same thing as the Lake of Fire. Yet the Lake of Fire is a result of men's evil choice to reject God. That rejection assigns men to be forsaken in the Lake of Fire at that point. Jesus endured the first forsaking by God. The second death with be a final forsaking of another kind - the Lake of Fire.
About three in the afternoon Jesus cried out in a loud voice,
"Eli, Eli, lema sabachthani?" (which means "My God, my God,
why have you forsaken me?"). Mat 27:46
Jesus remained forsaken until the last sin of mankind was yet to be poured on His body.