Be with the class from now on - Never lag behind from now on. You already have a lot of backlogs, it’s better not to increase it now.
Follow the divide and conquer strategy - Divide your days perfectly. Devote 2–3 hours each day to complete your backlog. The rest of the time should be exclusively reserved for present topics and homework.
Don't be in a hurry now - Don’t think that you can complete your “huge” backlog within a month. It will take time but if you keep believing and following things properly, the backlog will get cleared sooner.
Take up one chapter at a time - Start with your favorite subject. If you love Math the most, then take up the easiest chapter left and start solving it. Take your time but solve the material honestly.
The present is the majority, past is a minority - Your major time each day should be spent on solving what’s going on in class. It’s not that you will spend your whole day trying to clear previous work.
Make the best use of holidays to cover your backlog - Try to make the best use of holidays to clear your backlog, like the ones you will get after a big test in coaching.
Don’t panic and learn from your mistakes - There is no point in taking stress now. You have made a mistake but the good thing about all this is that you know you have made a mistake and want to correct it.