Is the hadith that mentions Allah commanding the angels to admit a man into Hell—whereupon the man says, "This was not my expectation of You, O Lord"—and Allah then commands his admission into Paradise, authentic?

The hadith (definition) referred to in the question is very weak due to Abu Dhilal, and it was deemed weak by Ibn al-Jawzi and al-Albani. A similar meaning was also reported from Bilal ibn Sa'd, but its chain of transmission is also weak due to Mansour ibn Ammar, and Bilal ibn Sa'd did not attribute it to the Prophet, peace and blessings be upon him. A similar, abridged version was reported from Al-Hasan (definition) al-Basri. The conclusion is that nothing with this meaning is authentically established from the Prophet, peace and blessings be upon him.