Well, that is the darndest thing. I was going to walk you through deleting partitions, re-initializing the drive, partitioning and reformatting. But the space just isn't there.
Personally, the first thing that I'd do is download diagnostics from the manufacturer - but I haven't even looked to see if Samsung provides them. This may be a defective unit, and there is an outside possibility that this is the second counterfeit drive we've heard about here. There used to be a fairly large problem with fake thumb drives.
I've asked for other storage experts to weigh in on this. I'd call or email Samsung with the serial number and 1) ask if it's legit, and 2) tell them that it arrived with only 125 MB of space and get their support. Best I can do.