Chittu
Yes, you can.
If the mistake is some vital that is affecting your marks or leading towards your disqualification, the teacher present there allows you to correct things.
As I am sharing my experience, I was writing descriptive for my CHSL paper, and one of the students in the class wrote Xyz at the place of the name while writing the letter but later he realized that the question paper has given a particular name for the letter, then he asked the invigilator for a whitner to correct the mistake and they were like OK. They arranged him a whitner.
So, yes you can use.
