i don’t know if this will work for you but what helped me when i had major assignments i needed to focus on was to eliminate everything that normally distracts me i would delete all games and social media from my phone i would block websites to any social media site or put a 1 minute time limit on them i would still get distracted but every time i was thwarted by all the blocks i set in place it forced me to at least try to be productive also your school should offer accommodations for adhd i’m not familiar with the paperwork but i do know the option is there if you meet the requirements you could be granted more time for assignments and tests you will have ask the school to get details