You could be logging in with a User ID different from the account you created your return in (the combination of your User ID and password uniquely identifies your TurboTax Online account, not your email address), or have multiple User IDs associated with your email address.
To see all your user ids:
Go to the TurboTax Online sign in page and select the I forgot my user ID or password link.
Enter your email address and select Continue.
A list appears with the user IDs associated with the email address you entered.