I can't stop calling Nargacuga Nicaragua, or Narcagua, but I agree that it is one of the most problematic monsters (still have to fight the remaining 6 star village monsters, though), but I insist is not as bad as Zinogre. Perhaps I have gone with that impression because I farmed Zinogre for a while for its plate (to no avail, btw).
Don't put performance pressure on yourself. You win the quest and all is fine. The time the game gives you is 50 minutes, so you are well below that. In Monster Hunter 3 Ultimate I actually failed a quest by running out timer. It was the helicopter monster, Duramboros. In the beginning I never got close enough to deal damage. That running out timer was made worse, because I already had him limping and going to sleep, but as I engaged him then, the time run out. So don't sweat if you need half the allocated time for the quest, you are doing fine. You are not speed running or something. If you feel it becomes too easy, you can put challenges on yourself, like killing it in under x minutes or whatever.