Hi deepali, you connect on the NTSE helpline number to understand if you can rectify the same.  This also depends on the region from which you are appearing for the exam. Ideally, one should enter the name as is written in the school records or Birth certificate. 

Here is the link to the contact details of NTSE, region-wise

http://www.ncert.nic.in/programmes/talent_exam/pdf_files/LO_list_2018-19.pdf

You can either call the authorities or mail them, as per the details against your state.