That is normal. Relax; we all make mistakes when writing everyday things due to time constraints and stress. Just keep in mind that they do not know you personally, and while I do not recommend making this mistake in the future, it is fine if you do it accidentally. Until your roll number or registration number is correct, nothing matters to the examiner because it is what distinguishes you and is assigned by the institution. All other details are consistent, such as two people having the same name in the same class but having different roll numbers. So cool.