I really need to control my overthinking.

I(16M) am writing this confession kinda at 12.30am. I never learnt to show my fears to the people i know or my family. You can say I am scared of showing my weaknesses to people. I don't know know what to call it, maybe insecurity or lack of confidence. Whatever. Coming to the point. I am currently in 11th (final exam remaining), my tuitions have already started 12th course. I got 91% in 10th with 100 marks in Standard Mathematics and 97 in science. I started my 11th late and only getting 75-80 marks in all subjects. My tuition teachers are confident that i can score in 12th. I want a simple seat in Institute of Technology, Nirma or L.D.C.E. I am in science stream and from Gujarat. I want Electronic and Communication branch. The approximate percentile required is 97 in Boards and Gujcet. I don't have any family pressure because i come from a really supportive family. I am scared that what if i couldn't achieve my dream. I am scared what if i am not good enough, what if I can't recall all the formulaes and stuff at the right moment when all of it matters. I am scared but not stressed. I really need to stop overthinking. I am so so so scared.