Booking time off of work?

so im 16, 17 next week and have a part time job in a restaurant. i have been working for about 6 months now. i normally do two 8ish hour shifts on the weekend, every weekend. but this month i have had my as-level exams, which are obviously really important. so i have booked off every sunday to allow my self to revise. so thats 4 sundays, and before now i have booked off about 4/5 days. but this weekend i need to finish work a little early, by about 2 hours, because i have to babysit.

but im really nervous that they will hate me and possibly fire me? because i keep booking off days etc.

its really scaring me, so would anyone be able to give me some advise on the matter, and also let me know how much time i am officially allowed to take off?

thank you