Hi 
As you know Tamil Nadu has the highest cutoff talking of which last year least marks to secure a seat in CMC  Vellore was 556 marks from your category under state quota ,so I'll say you don't have chances to get a seat in that college as 400 marks are too less but you can apply for deemed colleges to be on safer side . Remember that cutoff varies every year depending on number of students appearing in exam, difficulty level of exam, students scoring more than you and your category. Wait for the answer key till that time.
To know more about Cutoff of various colleges in Tamil Nadu click below 
https://www.google.com/amp/s/medicine.careers360.com/articles/neet-cutoff-tamil-nadu/amp
Hope this helps

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