Had the same problem you did. Here's how I did it.
1. Download the free app iCal Import/Export 2.2 from the Google Play Store.
2. Export your mycalendar to a file (mycalendar is samung's calendar)
3. Import the file into your google account calendar
4. Open your samsung calendar app and under calendars de-select mycalendar.
5. When you now post a new entry in your samsung calendar app make sure you tell it to use your google calendar instead of mycalendar, You may need to do this a few times to have new entries default to your google calendar.
Now you can still use the nicer IMO Samsung calendar app but it will only display/add to your google calendar instead of samsungs. You may of course double check to make sure the iCal app imported all your calendar entries, but for me this worked beautifully the first time around.