You can prepare for NEET alongwith 12th board exams. The syllabus of NEET comprises of chapters which you have studied in 12th or 11th, so it will be an easy task to manage them parallely. You have to manage your time properly as both exams are important for you. Firstly, make a blue print of topics which is common in both exams and then give your time to that. Know your weak topics, and give more time to them.

It seems to difficult to continue preparing for both tha exams but it is not impossible. If you will manage time properly, give equal priority to every topics, and believe in yourself, then you can surely do good in both the exams.

All the best!