You've got an 08, it's under warranty. Make the dealer fix it.
Is it always registering half full (or empty) or will it change as you drive?
If it's always at half, maybe a fuse or a loose wire on the sender and half is just the default position for the gauge.
If it's the float, you'd have to pull the whole sender, pump, float thingy majig out and that can be messy. If that float unit or the sender is bad, you'd have to BUY a new one. If the dealer does it, it's free.