Google Calendar sync back from Android phone?
Download iCal Import Export 2.2 from the play store and you can backup the calendar on your phone. Move the file to your pc and follow the instructions here: https://support.google.com/calendar/answer/37118?hl=en to upload to your Google calendar online.

Or maybe you can just turn sync on? That I don't know. But create the backup first if you try it!

Good luck