As per the instructions and help files for the creator, we recommend creating and logging in to your account before commencing your design. However if you missed this step, we do have one solution to try and solve the issue.
Ensure that you do not close, refresh or navigate away from the Online Creator window with your design.
Open a new browser window, and log in to your account (or create a new account if you need and log in). In the new window, log in to your account. When logged in, go back to the Online Creator window with your design and you should now be able to save the design.
Unfortunately we cannot recover any lost designs.