If you utilize time very well, you can surely do  well in your NEET UG Entrance Examination. Since you are now in 12th class, focus on class 12 subjects. Read NCERT thoroughly. You should study class 12 chapter in such a way that when your class 12 board exams get over, you no more have to study anything about class 12 and each and every concept should be in the tip of your tongue.

After board exams get over, you will roughly get 1 and a half months. It is this period where you need to study class 11 chapters along with solving previous year question papers and mock papers. During that time focus more on 11th biology and chemistry. And in physics just do previous year questions as you can easily get 100+ in physics if you have thoroughly completed your class 12 physics syllabus.

Dont lose hope, you still have time and you can do it. Any more queries, let me know in the comments.