I found that when I put only one piece (or 2 slippers in my case) into the washing machine for felting, they do not come out quite right. But if I put in an old towl, they get the propper friction to become felted.
You can refelt things, too. If the size is not yet right, maybe the felting process is not quite done yet. Put the piece back in and redo the cycle (if it still is too big!)
The last bit of fuzz you can shave as Jan said.
If you have no sweater shaver (not everybody will), you can use sharp scissors: Lay your piece flat somewhere, fluff up the fuzz a bit, lay the scissors flat to the surface, just a hair above the actual surface and cut carefully. Needless to say that a) you have to be carefull doing this and b) you have to repeat that one step on every bit of your piece, so it will be some effort.
Some fuzzyness is not bad on felt, though, so do not become over-concious about it.