Hello Ruby Kumari. Thanks for contacting Careers360 and we hope we will be able to answer your query. 

Please note that you must have passed class 12th examination or equivalent with subjects like Physics, Mathematics, Language and one of Physics/Biology/Biotech/Technical Vocal as compulsory subjects. Additionally the candidate must have scored a minimum of 45% (40% for category students) in each of the mentioned subjects.

But, I feel that you have little chances of actually getting a seat in BIT Mesra, because if the sheer competition and that your JEE Mains marks are too low. 

Please see this link for more information:

• http://www.careerlauncher.com/engineering/colleges/bit-mesra.html

Hope this helps you and all the best!