Is this a new flash drive ?
Quite often, if always in my case, the size of the drive is always a little less then it is said to be.
Yours being half the size cant be right though. As B00kWyrm said, check it in another system if you can to see if it shows the same.
I know it sounds daft, but double check that this is actually suppose to be 1gb in size. Check either the packaging if it's new or from whom you got it from.
It could also be possible that the full size of the drive hasn’t been partitioned. Go into device manager and check this.
Start --- run --- devmgmt.msc
You should see it listed under disk drives. Double click it, volumes tab and then click populate.
From here you will be able to see if there is any unpartitioned space on the drive.