im struggling so anxious about GCSEs exams this week
I was also in the same boat as you but then my teachers all told me that panicking would only lead me to struggle more.
Try to calm down a little. Some of your subjects matter more then other. Focus on English Language and Maths then on the subjects you chose for A-Level (if you want to those).
Most importantly, don’t try and cram. You’ll burn out and struggle in the actual exam. Get a good nights sleep before each exam. Eat well. Good luck on your GCSEs!