Hey,

If you start 3 months time is very less to get 250+ marks but it isn't impossible. If you are cleared with concepts of 11th and 12th class then it will be very beneficial for you.

These 3 months you should do both hard work and smart work too. If you are good in any of the PCM subjects then try to be perfect in any 2 within a month and for the other subject give 1 and a half month and half month for revision.

If you have completed the course 3 months prior to exams then start revising and solving the previous year question papers.