you must reach the board and clarify first

but in my view, if you haven't paid the application fee you can go with any of the username or email id you have registered and can upload all the documents 

or you can  try the below steps ;

• Click on the official website link. 
• Click on the “Edit CET-2018 Application” link.
• A new page will be opened on the screen.
• Now, enter your User ID and click on “Send OTP” button.
• OTP will be sent to the entered mobile number.
• After submitting the generated OTO, changes will be done.
• Now, make corrections in wrong details.
• Verify and ensure that all the changes done are correct.
• After modifying details, click on the “Declare Button”.
• Take the printout of the modified application form for further use

In this case you need to contact to the official. You can send them a mail on keauthority-ka@nic.in or contact on 080 - 23460460 regarding this.