With 66 percentile in JEE Mains as an SC category student, it will be tough to get admission in top NITs because their cutoffs are usually higher. But you may have a chance in some lower-ranked NITs or Government Funded Technical Institutes (GFTIs) that have lower cutoff marks.

You should participate in the counseling process and apply to as many options as possible. Also, consider good state-level or private colleges where SC reservations apply. Keep preparing for better chances next time !