Advice needed🙏

I am in class 12th and have to give jee , I haven't completed my 12th syllabus(45% is completed only) Now, I have decided that I'd devote time to 12 only till 21st dec and after that I'd start devoting 4 5 hrs to 11th. Is this the correct way ? And if yes pls give advice on how to do 11th and how can I complete 12th in a short span.🙏