hello 

khagendra hansda 

yeah you can get the seat in the NIT you should give the JEE mains exam and aslo you can give your exam in 2020 not at all problem 

My suggeestion to read the NCERT text books clearly and understand the concepts and 

then later on go for the Refernce books 

for physics please refer H C vema

for mathematics please refer arihant

for chemsitry refer the O P tandon

and also you refer the previous year question papers

thank you