Never mind, Chikky.  I know it's disappointing when you don't feel you did your best, but chalk it up (or down) to experience.   You'll do better next time and will be better prepared for those sorts of questions.

As has been mentioned, there are interview practice websites, which might be helpful. I did have a look at one from here in the United Kingdom and it was quite stretching.

Best of luck for the future.

Raindance