I understand you was over occupied with your scores in school that you neglected JEE preparations!
But understand school study and JEE prep are very much different. Don't panic. This happens with 20 out of 50 students. Students gets over confident with marks in school that they start presuming that their concepts are clear but what we have to know is anyone can score in school without knowing concepts.
Now when you have gathered enough courage and support, start building your concepts and kill the insect of over confidence from your mind.
But your scores are not bad and with more hardwork, you can do wonders!
Remember, now you have enough time and for entire coming year, your goal should be JEE only.
Wake up in morning everyday and plan what you have to study, what topics to cover for that day and try to devote 10-12 quality hours of study.
After spending day, see have you covered your tasks! If not, get a pace and continue. You need motivation dosages as evident from your habit of not doing.
Watch one TED talk everyday on YouTube. Try to watch inspirational video everyday. This will push you to work if you want success.
Remember, failures is what leads to success.