There’s nothing wrong with admitting a mistake. A human being is bound to commit mistakes. This time it is advantageous to go back as far as possible in the past and find an answer.

The advantage of doing this is that a youngster is expected to commit more mistakes than a mature and seasoned person. This would give an impression that since that time you have committed mistakes but not that big.

Take the word “mistake” as liberally as possible and go back to your student life to answer this question. Probably you can say, if I could go back to my student life, I would have studied Biology instead of Math.