What you must remember at all times is that a project can be saved only if you’re creating it while being logged in to your account. There is no way to save or restore a project that has been created without an account.
Once you’ve logged in, the rest is easy. The project is automatically saved with every change you make there. Just make sure you have a good internet connection.
Note: Please make sure your device is connected to the Internet every time you finish working with the project. If you work on the project offline, your changes will only be saved after you connect to the Internet. If you open the project from another device with an active internet connection before you save changes – those will be overwritten.