Hello student,
You have not mentioned which category you belong to  or your region. With 520 marks, you have chances of procuring a seat in the government medical colleges when comparing the results of previous years. But, if your category is general, then there would be a tough competition only. The cut off's for various region in general category were
AU region 533
SVU region 517
OU region 526
Also, one thing to keep in mind is that scores and ranks vary each year with difficulty level of the question paper and availability of seats. However you can go through the following link to know about the cut off's and ranks for the previous years and calculate your chances of selection
https://medicine.careers360.com/articles/neet-cutoff-ap
Good luck

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