According to your specifications there is really a great possibility for you to get a seat at NIT patna. Now if the number of vacancy left gets filled in 3rd counselling round then there can be a problem but you have a possibility of getting it.

I would also like you to suggest that you should prepare a alternative plan to be safe. So according to your rank , you should prepare a side plan so that if by chance NIT Patna is gone then you will have another way to reach your destination i.e., Mechanical Engineering.

I hope my answer helps you. All the best for your future endeavors!