Well it's possible that you did indeed get a 60 instead of a 80GB HD. Not likely but I'm sure that you could get it taken care of without much hassle.
However if you're showing 57GB with the default OS installed then your probably do have an 80. The default OS install takes up quite a bit of space and as you know a 80GB drive doesn't really work out to 80GB of space due to the fact of how drives are advertised and how they're actually measured.
If you're looking to reclaim so space and rid yourself of some stuff that you may or may not even use you might have a look at
THIS.