Disappointment and frustration at this stage is quite normal. As the exams come nearer, the mental tension increases and overall productivity decreases. While it should go the opposite way.
So first of all, calm down. There's time left. Forgetting concepts of several topics happens everytime. All you need is a good revision.
Start with solving the easier questions of EMI, Magnetism and Mechanics. You'll be able to solve most of them which will consequently increase your confidence.
Then you can approach harder ones. If you find difficulty in solving them, revise and read the notes, examples and reference materials or ask them here.
Planning your every revision in this way will definitely help a lot in your time management.
Please feel free to post as many doubts on our discussion forum as you can. If you find any question
Difficult to understand - post it here and we will get you the answer and detailed solution very quickly. We
are all IITians and here to help you in your IIT JEE preparation.
All the best !!!