Is it because of stress, anxiety... that I always get bad grades in math?

Hello ! thanks for anyone who will take the time and read this
Heres a summary if you don't feel like reading that much: Somehow, even if I perfectly understand the content and work hard I still get bad grades I'm not sure why. I tried my best to solve this but nothing seems to works
At the first year of middle school, I didn't prepare that much for math I took 2 hours of private tutoring and made past papers I still managed to get full marks throughout the year I was the first at my school to achieve such grades, however next year the content was much harder and our teachers, exams were similar to Olympiades so I started working so hard I took my regular 2 hours of private tutoring I understood all the content from the first go and every week I done an enormous amount of past papers I got so shocked by the grades I got after all the hard work .Still to I tried to work even harder I have done more past papers organised my time and re-done the past papers my private tutoring teacher estimated me perfect grades, but I flopped hard again and again and I worked harder again, I got to the point where I was OBSSESSED My teacher couldn't find a reason why I still got bad grades ESP that after the exam when I redo it at home on my own I get good grades. Last year, which was my third & last year at middle school, I started taking 4 hours of competitive math club and 2 hours of my math tutoring weekly . I had other things to prepare other than math of course so I didn't do as much past papers I have just done some interesting past papers weekly and math Olympiades + math exams throughout the year didn't matter that much so I didn't care that much however My grades improved but I still got disappointed. I'm not thaaaat intelligent at math, but you can say I'm on top of the average. so why I get bad grades this is my first year at high school and I want this to stop Its soooo disappointing for both me & my teachers Anyone I can relate to? or something I have been doing wrong? My first exam is on the 25th of October and I'm concerned that the same will happen .

I can relate and it's sooo annoying! I understand the class easily and then flop the test. My advice is to first, pretend that your not in the exam, and second, don't stress too much. If you are getting bad grades because your panicking, panicking more won't help (I speak form experience).

don't put so much pressure on yourself. Try and picture yourself at home or with your tutor, not sitting in that tense environment. I related to this a lot a couple of years ago, but my confidence grew when I started getting good grades because of my relaxation and breathing techniques. It may sound a bit cringey, but trust me, it works! Knowing everything and putting hours into practise isn't much help when the real problem is probably stress. Relax yourself. Hope this helps!

Honestly, I have never considered breathing techniques... I'll make sure to try it this time. Thanks, I think that once I get a good grade hahaha My confidence will grow so hope I succeed at least once ^_^