Hii Vaishnavi!
Don't panic. Event If you fail, There are always chances to improve. CBSE does provide options for improvement tests and re- examination of you fail in a particular Subject. You can apy for re- exam in the subjects you fail and can improve in them.
But, you need to focus and study well because you don't get such options again and again. Check on the official CBSE website for updates on re- examination and fill the application, when they are out.
Hope this helps.
Good luck!