Hello there,
First, believe in yourself. If you believe that you can do a work, then no one can stop you. And no it's not late if you start studying now. Try to build up your confidence, and stay positive.
Coming to your SBI exam, know your entire syllabus. Start studying for 1-2hours daily, since you said that you don't have a habit. Don't worry, just prepare yourself. Solve the previous year question papers. Give regular mock tests. Keep enough time in hand for revision. Don't worry, everything will be fine if you stay positive.
Hope this answer helps you.
Good luck!!