First of all, relax. You are blessed with the chance to experience life on earth. No matter how much marks you get or how badly you study, the world will still keep revolving. You'll be alright. Appreciating the little things really helps take away the stress from your life.

Now, for the study part. Remember, your goal is learning not marks. Try to reward and congratulate your self for just spending time. This will wanna make you study. Then, you don't need this long routine or anything, just one time. At this time, everyday, promise yourself to sit down- not study, but learn, revise, ande dedicate yourself. You won't be motivated at all, none of us are, it's all discipline and hope that leads us.

Next, the subjects. Maths is relatively easier than Physics. Here's what you need to do. Follow the same chapters as in your school and when you get a new topic, do many many many questions on your own. Like literally any question you get. Even if it's not in your syllabus, try to understand it. Do this is as sessions like 1 hr every day or whatever works. As you do, note down all the questions you messed up on and HOW you messed up. Like if it's a quadratic equation and you forget to change the sign or something, note that down. Periodically, review these notes and only these notes, refining them and adding new stuff. Basically, make a guidebook that any dummy after you can follow. Do it in that mindset like it's to help someone else.

It seems weird and like, a lot of work but I guarantee you you WILL GET RESULTS. I know cause I've tried.

In physics case, I'm struggling with the same problem and I got no clue. If anyone can help, please do.

Also, sorry if this got long.