As long as you've corrected the roll number it shouldn't affect your answer sheet. Your answer sheet will be accepted despite the initial mistake in the box.

Hello ASpirant

If you have filled the bubbles properly don't worry your omr will be checked.

There can be two scenarios that might happen,but the system is quite apt to deal with it

Let's consider

1. You have written the wrong roll no on the sheet but bubbled it properly,then the omr sheet reader will read it and will classify your results accordingly.
2. If you fill the omr wrong and write,right roll no on the sheet the software will read rest of your data and match your omr and then classify your results accordingly!

Regards!