Hello

For admission in st. John's medical college through neet as you mentioned you are a Catholic Christian so you can apply via all india roman catholic quota.

As the cutoff for the college are high according to previous year but it may change every year depending on various factors like no. Of seats, candidates applied

According to previous year cutoff ranges between 500-650 and if you are Christian so last year closing rank for roman catholic category was 44806

So according to all this you should score atleast above 500.