Hello dear student, 

As you said you have scored 55 percentage in your boards examination so dear student I hope you must be aware of the eligibility criteria for students appearing for neet which says you need to have Atleast 50% for general category student combined while for the sc/at students it is 40 percent. So you are eligible for neet . While if you have completed your 12th from CBSE boards then on the official website of CBSE there comes improvement forms and you can fill that . They will be asking you some information that you have to fill correctly. 

For any further information please feel free to ask anytime. I hope this was helpful to you.

Best wishes