See, getting admission in NIT with 46 marks depends on your state. If you are residing in Arunachal, then you might get Arunachal NIT. But if you are residing in UP, Delhi, or Bihar, then with 46 marks you won't get any NIT. For GFTI colleges, you can apply, that depends on the you are residing. Don't lose hope, as it doesn't cost you any money to apply for NITs. So do apply, if you can make it, then no one can stop you.  

Hello.

It depends on your rank rather than your score if you can get into an NIT. The marks vs rank keeps changing each year along with the cutoff due to various factors like difficulty level of the exam and the average score of students etc. You could use the rank predictor to get an accurate estimate of your rank:

https://engineering.careers360.com/articles/jee-main-rank-predictor

You could then refer the cutoffs of previous years:

https://engineering.careers360.com/articles/jee-main-cutoff

Hope this helps.