You have not provided enough information for anyone to answer. Assuming you bought a NEW cylinder for your bike, then no that is not the piston you need.
According to what I can find with a quick search, the stock bore for that machine should be 54.0mm. So at 55.07mm you'd be looking at .40 over, in which case it WOULD be the correct piston and your cylinder would obviously NOT be "new". Was the cylinder previously sleeved? Bored and re-plated?
/me grumbles loudly.
J.