Hello Aspirant,

If you do not have a roll number , then there must be some other number equivalent to roll number on your final mark statement, for example ,registration number, marksheet number etc. Also sometimes roll number might be given under a different name for example in ICSE marksheet , the index number is the roll number . So find out the same in your marksheet and use that. You can mail them once regarding this and seek their assistance in this matter. They may or may not respond , but give it a try. Anyways , you are allowed make modifications in the registration form for two times ,so in case you find out a right solution by the end of the application deadline , then you can edit it . Remember  this can be done only till the time you haven't paid the fees, and finally completed your declaration with 'I agree' and submitted the application.  In case you are not able to find any solution , enter whatever number you have have and then explain it during document verification process. But again , make sure that your roll number is not given under a different name in your marksheet.

All the best