I still remember it because I tend to pray the Rosary in Latin. I did cheat, however, to look up all the accent marks.
Now, there's another version floating around out there also:
O mi Jesu, dimitte nobis debita nostra, libera nos ab igne inferni, conduc in caelum omnes animas, praesertim illas quae maxime indigent misericordia tua.
I doubt that there's an "official" version, and I bet that both are just translations by amateurs, since I don't believe this is any official prayer of the Church.