pls help this girl out, guys

So, after wasting my 11th grade till now, I studied seriously this week and realized what caused me to procrastinate this whole time. Apparently, I’m slow—very slow. It took me almost 5 hours to solve just 30 questions in Maths. And when I am not able to do questions, specially in a row, i just feel like doing something else and it's usually the time when i pick up my phone and get distracted . (I have handed my phone to my mom till 13th march) How do I improve this? I want to score good marks in both school and coaching. In the previous test at my coaching, I got 104/300, and in school, I scored (out of 30):
Physics: 9.5
Chemistry: 7.5
Maths: 16
What can I do to make sure I don’t completely waste my 11th grade? By the way, my school annual exams are starting on the 24th of February and will end on the 13th of March. At my coaching, 12th-grade classes will begin in April, and that’s when we’ll have our reshuffling test for the 12th grade. What should I do? How should I study, and what should I focus on to make the best of my situation?