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.
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