You haven't mentioned your Category. Nevertheless, in 2018 under State Quota, the cut offs for various Categories have been as follows:

General Category: 420

OBC: 325

SC: 343

ST: 264

ST Plain: 264

ST Hill: 217

Now this is 2018 data and cut offs change every year. Cut offs change every year depending on various factors such as no.of Candidates appearing for the exam, no.of Candidates qualified, top NEET score and difficulty of the exam. So ideally a score of 550 can get you a seat in Assam. Regarding your aggregate in Physics, Chemistry and Biology, your 12th marks are only required to qualify for NEET. But for as seat in MBBS, it is your NEET score that matters.