We completely understand what you must have felt after not getting through the top most B-schools. To look back, you could have tried in the other good B-schools too. Only completing bachelors is not going to be sufficient, you will have to team it up with masters in order to get better career opportunities.
Creative department in advertising includes professionals like copywriters,scriptwriters,visualisers etc and to get in to the field, its important to note that candidates with a degree or diploma in mass communication / advertising / social communication are found suitable. SO you can either take up a course in these or take up MBA in marketing which is also one of the entry route to mass communication.
For more information on advertising as a career you can log on to http://www.youngbuzz.com/careers/career-options and check the section on media and communication.
Hope this helps.