I got 21000 rank in JEE Mains general category. Should I drop for next time or go ahead by taking any NIT or BIT, Mesra?

Yes, JEE Mains has been listed as an accepted entrance exam for MIT Academy of Engineering BTech admission. The institute has also listed MHT-CET as its accepted entrance exam. Thus, candidates with a JEE Mains score can apply directly without appearing for MHT-CET.

CT Group of Institutions (North Campus) offers scholarships to students who crack the JEE Mains exam. Institution offers various scholarship categories including merit based aid for exceptional JEE Mains performance. 

Guru Nanak Institute of Technology accepts JEE Main scores for admission in BTech programme. However, it is not compulsory. Aspirants with WBJEE or CE-AMPAI scores can also get admission in BTech provided they also meet the eligibility criteria.

Students who gave the JEE Main session 2 exam and want to take admission at IITs should start preparing for the JEE Advanced exam. Students with a more than 98th percentile should start to study for the JEE Advanced exam.

Those who have secured a percentile between 95th and 98th should focus more on

With a JEE Main percentile of 90.94 and CRL rank ~1.4 Lacs (female, general category), you have realistic chances in mid-tier NITs (later rounds), state government colleges, and strong private universities in Tamil Nadu and Bangalore for ECE/EEE. Top NITs/IIITs are unlikely, but good regional option