For your vote to qualify for counting, the Ballot Paper Number must correspondence with the number stated in Form 2. This is to identify that you have been issued the Ballot Paper.
If you find errors on Form 2, including the Ballot Paper Number, you may amend it by writing down the correct information beside the wrong one, and get the witness to sign beside it. Your vote will not be spoiled for making amendments on Form 2.
HOWEVER, do NOT make any amendments on the Ballot Paper as it may be counted as spoiled vote.