Hello.
If you want to cancel your improvement exam of your class 12th and you have filled this form then there are two chances one is that if you have filled the form but you didn't  pay the fee in this situation you can just leave it then it will be cancel by itself but you will receive a  notification letter from the board and another situation,  when you have also paid the fee, in this situation you cannot cancel this even if you don't attend the exam fee will not refund.
Best of luck.