Overthinking about my grades

Ever since I'm young, I always believe that my worth is based on my grades. Now that I'm in highschool, my grades are dropping. I tried my best but it's not enough, I'm not enough. I'm scared that once my place on top students list drop, my parents will get disappointed and my classmates might tease me about it. I've been overthinking the outcomes for days. I need to share this to lessen it a bit, I guess.