hi,

yes, you may certainly get private and state government colleges in btech course, but for nits , iits, gftis , it is required to have 75%  (general category)aggregate marks in 10+2 course, for sc/st candidates it is 65% marks in aggregate in 10+2 course, so right now focus on coming entrance test and try to get good score.

Admissions in btech courses are done on the basis of jee mains or other entrance examinations... So if you are getting a good eligible rank, your class 12 marks doesn't matter much... Until you are passed with a minimum percentage of 45-50% in India. Also, college is decided on the basis of your rank... So prepare well.