1-You need to practice for NIFT CAT exams from sample papers which are available online.
2-To improve your drawing skills- Practice, practice, practice.
Your have scored very less in 12th so it is very difficult to get a seat in J.J College of Architecture. I will suggest you to look for other colleges
No, physics and chemistry is not asked in the NATA paper.
For your reference, you can go to the learn section to know which topics you have to prepare for the NATA Exam.
It will better if you write an email to DTE Maharashtra citing the technical glitches you are facing while filling the form. They are in a better position to guide you properly.
Firstly go through the NATA syllabus and previous year papers just to check what is your current level of preparation.Then list down all the topics in which you are strong as well as weak. According to the syllabus start working on your weak topics, here your main focus should be on concept building and clearing the basics.
When you are done with the basics then jump on to the advanced part, solve previous years NATA papers available on DQ Edge and work on speed building. When you are sure that you are done with your preparation start giving mocks and analyse them. Analysis of mocks is very important, if mock test is of x hrs then spend 2x hrs in the analysis part.
For detailed study plan and tips required to prepare for the NATA Exam and other entrance exams, you can visit Article section of DQ Edge.
Whether you will get a seat or not depends on a number of factors like:
1.Board(Gujrat board or other for CEPT)
5.score in 12th board
You have a good NATA score and 12th score, I'll suggest you to try and see where you stand in the rank list