microSD card falsely showing as full

Hi,

I have a 64 GB microSD card inserted into my MacBook, and Finder says I have only ~3 GB available, when I believe that there should be more storage space available on it than that.

When I right click the drive in Finder and 'Get Info', the drive info window claims Capacity: 63.83 GB, Available: 3.23 GB, Used: 60,602,843,136 bytes (60.6 GB on disk). When I browse the drive in Finder (I even have hidden files visible) there are only six items (3 application bundles/packages, and 3 folders), which are everything that I placed on the drive. Selecting all of these 6 items and right clicking to 'Get Summary Info' calculates 34,254,435,658 bytes (49.44 GB on disk). I have emptied the trash.

Why am I not getting all of my expected storage space? Why is there a discrepancy between the amount of storage space believed by Finder to be used by 'Getting Info' on the drive vs. by selecting all the content on the drive and 'Getting Summary Info'? What exactly is the difference between disk space used and disk space used on disk, and why is it such a large difference (~50 GB vs. ~35 GB) when viewing summary info of all items/folders? And why even with accounting for the ~50 GB of data used on disk is there a missing ~7 GB from the total 64 GB / ~60 GB 'on disk' capacity?

Other info: The drive is in ExFat format. The computer is a MacBook Pro w/ Retina Display, 13". The current OS is Mavericks, but I think this problem was already in OS X before the Mavericks "upgrade" (if you can call it that; side note, Mavericks sent my performance to crap with Photoshop and some other fullscreen applications... and Finder windows are glitchy on moving and scrolling..). The drive is: SanDisk SDSDQUA-064G-U46A Ultra 64 GB microSDXC Class 10 UHS-1 Memory Card 30MB/s with Adapter

Thanks,

-Daniel