Think of this as ‘all I had “left” to do’, or ‘all there was for me  to do’ - not so much emphasis on an obligation being conveyed as defining the last unfinished thing on the list of work. In English we readily use ‘had to do’ in both situations, despite the ambiguous meaning. 

Remember, this is a French to English translation, so the French is ‘correct’, it is the translation that may be able to be modified/improved.

Maarten is right: it's not an obligation as much as it emphasizes how little there was left to do.