Hello student, a score of 306 is a very low score even with SC category reservation. The cut off marks for SC category for MBBS in the year 2018 was more than 450-500 for most of the colleges all over India. The cut off marks change every year depending upon the difficulty level of the exam, number of students appearing for the exam, etc.  Therefore, the chances of admission in the SC quota for MBBS are very low. 

Good luck.