hi,

see yes its possible to again appear in nios and appear for jee main exam, but see while you would go for placement in colleges after completing the first three years of engineering, you have to justify , what you have done in these years. if you again appear in nios 12th exam, you should not show the previous 12th result, then it would be counted as gap of years, so  recruiter would ask you about the gap of years and as per different company rules you may not eligible for some of the organization for recruitment exam.

so if you get a tier 1 college this year, private or government, you should go for studies with out any more delay.

To know about complete list of probable college name, based on your score, category please use Careers360 college predictor tool,

https://engineering.careers360.com/jee-main-college-predictor?icn=QnA&ici=qna_answer