Hello

No, you don't need to give your 12th /2nd puc again..

You can just prepare for your CET and then appear for it next year .

Follow the below tips to prepare well for your CET examination

******* First of all go well through the syllabus of your examination

******* Make routine or timetable :- you can make a routine as well to avoid procrastination  , your routine should revolve around things i.e study, revise and practice

******* After completing each chapter , you should go through questions  of the same chapter

******* Make short notes of important formulas and concepts for each chapter and Keep revising it

******* Solve previous  year questions of your exam  :-it will let you know the examination pattern, type and difficulty level of questions, also concepts behind the question often gets repeated, so you should definitely solve previous year papers

******* Go through  mock test papers of your exam , it will let you know your preparation level and and weak areas so that you can work on them and perform well in your examination

Thank you