Hello Urvashi,
You do not have to worry at all, if you have written the correct roll number at beginning of your OMR sheet the person checking this will take care of it and enter the correct one in the system. It is not going to affect your results at all. If you are still worried you can mail the NTA exam body at neet@nta.ac.in. If you need other contact details you can visit their official webaite and reach out with you concern, the will reply.
All the best

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