Hello

As you have dropped a year thus you already have the knowledge it's just you need to channelize your knowledge in one direction using good books. Rd Sharma for maths and hc verma for physics and for chemistry 11 and 12th books are enough but for questions you might take up modern book for chemistry. Also don't forget to take up atleast 10 -15 previous year question papers which have solutions. Remember that results of derivation of physics. There are some direct questions on the results of derivations. 

All the very best