Though it is not the enough time period to start with one of the main engineering entrance exam but it depends on you if you can make thing achieveable.

You can cover up your NCERT which is the main books for your basics and hence you can reach up to all difficult questions. Because the time is less so you have to really work hard and systematicaaly.

Your study plan has to be made prioritizing the topics accordingly. You will have to go through previous year papers. you can work upon important topics in each section so that you can cover up those at first and if time allows you can shift to other topics as well.

Important topics in Chemistry:

Mole Concept, Equilibrium, Liquid Solutions, Chemical Kinetics, All of Inorganic is equally important, Benzene, Aldehydes and Ketones, Amino Acids, Perkin’s Reaction.

Important topics in Physics:

Thermodynamics, Current and Electricity, Wave Optics, Atomic Structure, Rotational Mechanics

Important topics in Maths:

Limits and Continuity, Maxima-Minima, Definite Integrals, Parabola, Circles, 3D Geometry, Complex Numbers, Probability

Give online/offline mocks to get hold over the subjects you have studied and don't miss out to attempt that.

Good Luck.