If you've not adjusted for the temperature of the wort then this might explain a few points difference.

  Check what temperature you hydrometer is calibrated to (usually 20°C/68°F) and then use this calculator - http://www.brewersfriend.com/hydrometer-temp/

  A 40°C wort would explain a 1.060 gravity being read as 1.055

If you've not adjusted for the temperature of the wort then this might explain a few points difference. Check what temperature you hydrometer is calibrated to (usually 20°C/68°F) and then use this calculator - http://www.brewersfriend.com/hydrometer-temp/ - A 40°C wort would explain a 1.060 gravity being read as 1.055

Another possibility is the kit is just overstating the potential OG. My kit suggested 1.042, but I have just put my ingredients list into http://www.brewersfriend.com/allgrain-ogfg/ and got an OG calculation that was very close to what I measured.