I am sorry that you are having trouble syncing your device. It is possible that your device has just marked that activity as sent already. You can try force sending the activity by following the instructions here: How can I resend my history from my wireless ANT+ watch to my computer?
If you are getting an error while syncing, you can try the steps in the FAQ What can I try when my ANT Fitness device will not sync with Garmin Express?
If you are still having trouble, it would be best to contact Product Support by phone.
