Since you have studied biology in class 11th as well as 12th. But in 12th it became your additional subject, you can give the NEET exam. Because as per the NEET eligibility criteria, student must study biology in both the class as main subject or as optional. 

Hello Rudraksh,

Candidates who studied Biology/Biotechnology as sixth subject in Classes 11 and 12 with practicals in Classroom mode in regular school and have consolidated marksheet of Class 11 and 12 containing Biology/Biotechnology marks.

Eligible for NEET 2018 as they have undertaken regular and continuous two years of study of Physics, Chemistry and Biology/Biotechnology along with practicals taken together in Classes 11 & 12.

So, You are eligible for NEET.

To go through the detailed information on eligibility criteria you can refer to this link- 

https://medicine.careers360.com/articles/neet-eligibility-criteria