Hi, you do not have to sweat over it so much as everyone who enters this field will have a rusty mind when it comes to studies because of big vacation gap. If you wish to prepare yourself for the basics you can find them on YouTube. Basics like differentiation, Integration and Matrices will be there in your first 4 semesters. You do not have to go for GATE level questions just take out your 12th math book and start from there only that much is needed. Your faculty members will guide you anyway. For electrical or electronics you should know some basics of physics that you were taught in 12th. Hope this helps. If you still have doubts please feel free to comment.