If you have had your device plugged in to your vehicle prior to completing the online registration it will still store all of your trips, it just wont know where to upload them to when you first plug it in.
As the device expected to be registered when first purchased, it doesn't upload trips in the same session as registration as it doesn't expect any trips to be on the device yet.
All of your trips will still be saved on the device! If you just plug it out of your computer for a few seconds, then plug it straight back in, it will begin the upload of your trips!