If this is about NEET, without causing you any scare, we will try to come up with some numbers. Every year approximately 14 lakh students appear for NEET and this year, it has been understood that for every 1 seat, there are approximately 20-25 Candidates competing. With that sort of competition, not to discourage you but any amount of preparation might seem less because you have no idea how the rest 14 lakh students are preparing. So unfortunately you cannot equate your preparation to the marks. Having said that, you are on the right track, trying to solve sample questions. Nothing beats practise. Continue preparing from NCERT and try to attempt one mock test a week. Just not solving those questions but also keep a track of time that is taking you to solve a question. Also keep a score of the marks that you are scoring in every mock test. Have post its with important formulae and periodic table so that you will have all important topics withn your reach even if you forget something while practising or reading.

Now regarding scoring 650, it means that out of 180 questions, you should get atleast 160-165 questions right without any place for incorrect answers. So in short you cannot afford more than 10 wrong answers which is a huge task in its own. Keeping aside the practicality of this situation, you should concentrate on the present to aim to get the numbers mentioned here. We have NEET preparation course if you want to prepare on your own. https://learn.careers360.com/knockout-neet-may/