pls offer some advice

this year will be my first time going thru exams like this, we currently have mocks going on, my anxiety is at an all time high, and im scared i wont make it, the pressure of it all is so immense and i feel so alone and helpless. my school is terrible at management and all the exams in the mocks timetable are back to back with no gaps in between. i dont know how im supposed to complete such long syllabuses every single day and sit in the exam hall the next day and still be expected to get good marks. please offer me some reassurance that everything will indeed be okay. im only 15, im just a kid, why am i giving exams which determine my adult life when im not even an adult myself?