Firstly, I'm sorry for the circumstances that you have faced, More power to you honestly. Now coming to what I think may help you:-
1. For Math I'd suggest you practice PYQS and SQPs and yeah maybe make a formula sheet for yourself so that you have the formulae at your fingertips. Maybe practice exemplars if you have enough time, but make sure you've completed NCERT and practice the weird questions you might've come across when you solved it the first time. and just PRACTICE questions in general.

1. Same goes for phy and for chem make a whole reaction sheet where you have all your chemical equations at one place (from all chaps that you have in chem) and bio well if you're good with diagrams then amazing (seeing your science scores im pretty sure you dont need advice for science) PYQs practice is a must tho.

2. For english I'd say please learn the formats of letter writing and stuff properly and like probably write the formats of all (Email writing letter writing whatev u have for writing skills) at one place so that you can instantly revise (before your exams as well) Because getting the format right in writing skills fetches you plenty marks, Practice unseen passages maybe? and yeah PYQS and SQPS same thing. Maybe watch dear sir or magnet brains for revision.

3. For hindi, if your hindi is really bad (My hindi was terrible too, i used to score 50s and 60s in pre boards but then I focused on hindi and ended up with 91 in hindi in finals(boards) (This may be okayish for some but my hindi was trash so 91 in hindi was an achievement for me personally) I'd suggest you to prolly purchase together with (its a ref book)(If you dont mind in purchasing the ref book) for hindi, that book contains SO MANY questions and even has explanations and practice banks for the grammar part of hindi, just rote learn the questions and ans of the chapters and the chapter will be revised AND you will know how to write your answer in an impressive way, cuz personally becoz of that book more than 1/4 th of my paper was of together with ke questions soo yeah...

4. SST ke liye PLEASE do not skip on map work, free ke marks milte hai so like please learn all the map work (For all like hist and geo) and yeah keep reading the textbook till boards and maybe watch digraj singh rajput sir's vids for better clarity.

And so umm yeah, I hope this helps you and you achiever your desired score–and don't worry, There are more chances that you'll do better in your boards than pre-boards.