It is quite unreasonable and unrealistic on the part of firms to expect someone to produce 100% accurate work products right from the word go, especially if the person in question is a fresher. Even partners make mistakes in their work, I have seen partners and principal associates make spelling mistakes. The problem is most firms do not want to invest in training their associates with a long term retention strategy.

I can assure you that you weren't as good as you think when you were a fresher. Someone put up with your ass and taught you. Now you do your bit. Circle of life.