Hi 

You have to fill the name as written in your class XII or equivalent examination marksheet.

In case, the authorities of BITSAT see any discrepancy in your application form, you will get a chance to make changes in the application form from March 15-19, 2018.  

You can refer to the link given below to know how to fill the application form :

How to fill BITSAT application form 2018

Hope this helps you! 

You have to fill your name as written in your 10th class marksheet.