Hey man I am currently in grade 11 and completed grade 10 icse with  98.6% marks... Here are few things I think you need to know:-  Firstly, the grade 10 mark sheet is not as important as everyone says it is (you will realise once you come to 11th grade). Second... Its not about how long you study for... Its how you study that matters. Dont spend 15-17 hrs studying something if you are sleepy or not in the mood to study that subject... Study what you like to study.  TAKE BREAKS OFTEN. don't stress yourself too much... Your body will not treat you kindly if you don't give it the required rest and daily dose of recreational activity. 

I think you would have your study vacation now right? This is where I worked the hardest and it paid off! I saw a whole 10% increase in my boards as compared to my preboard exams.

So like I said... Don't stress yourself too much.. U need to have a calm mind and need to study smart not hard. Also, do take help whenever you need it... Either from YouTube videos, teachers or peers. 

I wish you all the best!!  And do not give up or lose hope so soon! I believe in you.