NATA

No, you cannot get any changes in drawing section.

I believe that for JJ College of Architecture, you must secure a score above 155.
But the paper for NATA was easy this year, so nobody can predict.

2017 cut-off for JJ college was 150 in NATA.
It is a government-aided college. It is good if you start preparing from 11th, you will not get burden in the last.
All the best dear.

For JJ College, you need 150 marks in NATA as per their cut-off. But still, there are chances to get admission as you scored 92% in boards if you talk to them.
All the best.

You need 70 marks in NATA to get qualified for good college. You at least need 100 marks. Below that is also okay.

You need minimum 150 marks in NATA and 70% in 12th boards.

3-4 Lacs for architecture.

In order to get admission in top colleges, try to score more than 120 in NATA entrance exam. So, you can try in a good college, because you might get top college.

I don't know about IIEST Shibpur as it will obviously factor in your JEE Mains AIR (paper 2 if yo're going for B.Arch and to secure a good AIR with 57% in chose is not possible. (I think they set the minimum cutoff at 60% to appear for counselling). Even though to GET Architecture in JU you need to merely give the NATA exam (the score is irrelevant), even JU has a minimum cutoff of 60% in boards. I'd suggest, if your board permits it, appear for an improvement examination.