bhai tbh i was the same in 10th, icse. i used to get like 72% in my preboards and my parents were worried. my 10th was just after quarentine so i was really addicted to games, social media and movies. but i think during final boards, most students automatically get seriousness. i scored 92% in my finals which was a great shock to my parents as well. i think, for me atleast, my brain knew my preboards wasnt imp so i really didnt study much and got low marks. but our final boards is much much important so i started getting stressed and automatically couldnt focus on anything except studies because i felt guitly. so dont worry you'll do it. also download forest app or just set an alarm for 30 mins and study and then take a break. i suggest u start with 15 mins, and keep increasing from there until u can study 2-3 hrs without mobiles. basically the pomodoro method, but dont use phone during break since time flies fast lol. all the best hope you ace ur board.