Hello Varshita,

Hope you are doing well !

To answer your question, NO, single sitting BBA won't be valid to write exams.

Because for CAT you need to complete a minimum of 3 years graduation from any recognized university, with a minimum of 50% (45% in case of SC, ST, OBC, PWD). And after that only, you are eligible.

Hope I answered your query.

Thank You.