I have attached a screenshot of what the fenix 2 should look like when adding it to Express 3.0.10.0 for Mac. Make sure you're using the latest version of Express.
Open Garmin Express
Click the Garmin Express menu in the Apple menu bar
Click About Garmin Express
Click Check for Updates and install any updates to Express
If you still see the incorrect device image, unplug any Garmin devices, restart the Mac, plug the fenix 2 back into the Mac and try to add it to Express again. If you continue to see the incorrect image, please contact Garmin support.