You're not the only one. I myself have been worrying SO much. And I mean SO MUCH. But here is what I've been doing to kind of calm myself down about the whole situation...
1. You can always retake it! It's totally fine, yes next year the grade boundaries may not be as low or maybe even next year they will be easier! That's the beauty of maths - you can always retake it. If you fail this summer then you'll have another entire year to refresh yourself and become a master at maths and even achieve a grade of two higher due to that much extra time.
2. Watch maths videos. I love mathswatch, you have to pay for it however a lot of schools pay for it for their students, if you don't have an account then ask someone to borrow theres - there's not personal information or anything. It's an amazing site, it's like having your own maths tutor with you. I find that video help me so much.
3. Past papers and practice. In year 10 last summer during out past paper mock exams I was literally getting 6/7/8/9 marks out of the ENTIRE paper. Then at the beginning of year 11 in November last year I started doing past maths papers, watching a mathswatch episode every night, practicing and getting a voluntary sixth former helping me twice a week - now I'm achieving up to 50 marks in the paper and thats only from that 4 months of super revision. (the marks are out past papers which are fairly easier than the new 9-1 HOWEVER... this leads me to the next point)
4. The grade boundaries are going to be super low. It sounds as if almost every student in year 11 right now is struggling with the new 9-1 GCSE maths. This is ind of a good think because that means AQA etc will be lowering the boundaires - after all they wouldn't want England to go through the shame of having 90% of their students failing maths. A lot of my maths teachers at school have said all you need to get is at least 25 marks on all three papers to achieve a pass.
5. Find out which paper you are most suffering in and practice the topic within the paper. I got 30 marks in the two non-calculator specimen papers that we did in February but only 18 on the calculator - this is weighing me down so now I'm going to revise all that I can of the topics only in the calculator paper.
6. Learn the basics. In november I didnt even know how to add multiply or divide fractions. I didnt know how to divide with decimals. I didn't know the long division method. Now that I do I AM SO HAPPY because those basics help me answer SO many more questions!!! I love long division - BLESS LONG DIVISION.
7. Master one topic before moving to the other.
8. Find the best method for a topic. there's two long divison methods, the bus stop and the other one which is super detailed (times, divide subtract etc) and i find the second one is easiest for me. go with the easiest method.
9. do as many past papers as you can and look at the mark scheme afterwards. then you'll know how to lay out your workings out to get those marks.
10. if its a circle theorum question or angle theroum etc. and you have NO CLUE what to do then if you have time then write down ALL the theorums you know i.e a cyclic quadtrialteral has opposite angles the same (i cant quite remember). sorry my spelling is bad now because im trying to type as much as i can!! in my mock i had a question like this, didnt know what to do, however i wrote down the theorums which i thought would be relative to the question and I got an extra mark!!
hope this helped! i understand where you're coming from, Ive cried at least 10 times this month stressing over maths but when you actually think about it you dont have to worry too much because there are so many solutions to the problem.