Stoichiometry Chemistry Lab: Copper (II) Sulphate Pentahydrate and Iron Single Displacement Reaction?
Your results are actually very good.  The reason for thoroughly washing your copper is to remove any residual water-soluble un-reacted reagents.  If the copper were simply dried by sitting in room-air, the bulk of your extra 6% could still be water.  That's only 70 mg or 70 ul of water.  They way you produced your copper would likely result in a high-surface area product which can be tricky to dry.  Ideally, you would do multiple rinses in hot DI water then dry overnight at 105 C (really 70+C should do it).  If your yield goes down just a couple percent or so, you can still verify the excess water theory by repeating the drying.  If your yield goes down again then you are just having trouble getting all the water out.  Make sure you cool the copper, in a desiccator, before weighing.

If you don't have lab time for this here's what I'd try: take you copper home and put it an oven on low, about 200F or so, for several hours.  While still hot, place in the smallest reasonably air-tight glass jar you can find an get it back to the balance ASAP!  Good luck!  Oh, and NEVER touch the copper with your sweaty, oily fingers ;-)