To sync a Google Calendar to the Dashboard, you need to use the calendar's iCal URL.
Follow these steps to find and copy/paste the iCal URL in the edit Calendar and then process it to begin the sync.
Login to your Google account, navigate to your calendar, and click the 3 dots next to its name:
Scroll down on the proceeding page until you find the "Public address in iCal format" field, and copy/paste this into the iCal URL field in the Dashboard.
Copy & paste the URL you found in Features > Events > Create the Calendar or Edit.
Save by clicking Apply / OK.
Click Process Calendars at the top to begin the sync!