My MAT composite score is 512.88.....what will be the next step to get admission????

Hy
Your score is well above 500
As you can see, the MAT cut off of yours is 512.88 However, there is a caveat. The cutoffs of the top B-schools accepting MAT scores is only an indication of the quality of students the institutes look for admitting. Apart from the cut offs there are various criteria for shortlisting and selection such as past academic records, work experience to name a few. Hence it cannot be guaranteed that obtaining the cutoff percentile will ensure a call from the B-schools you have applied.
I am giving you one link where you can check your college at score above 500.

https://www.google.co.in/amp/s/bschool.careers360.com/articles/top-b-schools-accepting-mat-scores-and-cutoffs%3famp

Cheers !!