Hi dear ,

              Admission in colleges  and branches accepting JEE main 2018 depends on rank of the candidate and cut off of the institute. These institutes include NIT's ,IIIT's,GIFT's and other state government colleges and universities accepting JEE mains score. You have very less score in OBC category so you are neither eligible for any above mentioned colleges nor the core mechanical branch  thus you cannot get admission in mechanical engg.through JEE Main rank. Try for good private colleges.

All the best.