It’s hard to say how many you need to have correct to get AIIMS Delhi.

For Delhi, you need to be in the top 15 of your category rank which might correspond to an overall rank below 800-900. Now as AIIMS do not release marks corresponding to rank, it’s hard to predict. But based on my personal experience and talking with juniors, I believe you must score 125+ atleast to stay in the race. 

So you need to have almost 140 questions correct so that even after negative markings the mark stays in the range of 125-130.

All the best !