Hi Deepsha,

IIM Calcutta will provide an 'Application Correction' window most probably in the last week of September. So, you can rectify whatever mistakes you have made while filling in the application form. To know more about CAT 2018 registration, visit CAT Registration 2018

Good luck. 

Do not worry. You will be able to edit it later.  And in case if you mess up there, there will be provisions for the same once GD-Pi-Wat processes start. Like last time when IIM-Rohtak was conducting interviews for CAP, they allowed candidates to mail them about what mistakes they did, and then in the further rounds when document verification was done credentials were recredited.

After submitting the application form you will be allowed to correct your application form on select fields like percentage of marks, work experience and programmes selected only, Other information can not be edited  I would suggest you to mail this concern to the official.

Good Luck!