Have you reviewed the CSV guide?
Importing Your Data Into Fuelly
Also, a few more questions:
Which version of Gas Cubby are you exporting the CSV from, Free or Pro?
If you have Gas Cubby Pro, logging in by clicking "Set Up Sync" and logging in with your Fuelly username or email address is the best option.
If you have Gas Cubby Free, if you can wait less than 2 weeks, syncing is coming to the Free version. You may have received a pop-up in the app notifying you of this.
If you still need additional assistance, please send the CSV file to
support@fuelly.com and I will see what I can do to help. It will be sometime tomorrow before I can assist with this.