There is supposed to be a little 'stick on' pad on the back of the lever-like latch that holds the cover in place. Perhaps it fell off? If so, I'd just wrap the latch with a few turns of cloth electrical tape.
And yes, the Volt is an awesome commuter car. We have 21k miles on ours. I've only added about 8 gallons of gas since new - mostly because of FMM.