Hey admission in SASTRA university does not entirely based on JEE Mains admission is done on two bases

Stream 1: JEE Main 2018 and normalized 10+2 scores will be taken together for admission under stream 1. The scores of JEE Main will carry 25% weightage and 10+2 scores will carry 75% weightage. The combined scores will be used to prepare the rank list and candidates will be invited for admission on the basis of the rank list. 70% of seats will be filled under stream 1.

Stream 2: Candidates will be considered for admission based on their normalised aggregate 10+2 or any equivalent exam scores. 30% of seats will be filled under stream 2.

According to your JEE Mains rank and 10+2 result you must qualify for SASTRA university. So apply for it and wait for the final list.