To add the college calendar from Gateway back into Google Calendar follow these steps.
First login to Gateway and click on the calendar option.
Then click on the export button to the right.
Select what you would like to have included. Then click generate URL.
Copy the generated URL. (Not the one in the picture below)
Open Google calendar and click the Plus next to Other calendars.
Select from URL
Paste in the previously copied link and click Add calendar.
Then go back to your calendars and you should see the new calendar added.