Yes there are few chances for admission to BHU as you mentioned you belong to an open category.
BHU is taking first time admission through NEET entrance exam for BAMS program so it would be tough to tell you the exact, you can try with this score if possibilities are there.
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If u got the 403 marks in NEET means 100% surely u will get the seat in this college no doubt at all actually the cut off for the general merit catagory is above 350 marks so i can strongly tell u that u will ge this college