Hi,

Eligibility for Admission to NITs, IIITs and CFTIs participating through Central Seat Allocation Board: Admission to NITs, IIITs, and CFTIs participating though Central Seat AllocationBoard will be based on All India Rank as explained above subject to the condition that the candidate should have secured at least 75% marks(For GEN and OBC) in the 12thclass examination, or be in the top 20 percentile in the 12th class examination conducted by the respective Boards.ForSC/ST candidates the qualifying marks would be 65% in the  12th class examination. 

You are not eligible to get seat using jee mains rank since you don't have 75% marks. 

If you are not taking a drop year then here are some good private colleges:

• Manipal
•  SRM 
• KIIT
• VIT
• BMS Bangalore 
•  RV Bangalore
• Techno India University at West Bengal

All the above colleges have good placement in cs branch
To get more knowledge about your chance of getting a college please check the college predictor link below:

Https://engineering.careers360.com/jee-main-college-predictor

Thank you