No bro it’s easy to score 650+ in 100 days but on only one condition that by this time you have covered every chapter of physics, chemistry and biology.
Now I would like to add few more points:—
1.Make list of all chapters of physics , chemistry and biology on a page divided into three sections.
2.Read your coaching notes and solve previous year questions related to that chapter and tick that chapter on that page means you have done that chapter. This is the approch for physics.
3.for biology you should be thorough with every single line of NCERT and solve PYQ of that particular chapter.
4.for Chemistry
Physical -practice PYQ and read notes