Agree with SAS and FD - sounds like you're too fast down the approach; that's the only reason it'll float when it should land - but at least it sounds like you're flaring it properly, not driving it on nose-low as so many 172 drivers do - until one day the noseleg says 'stuff this for a lark' and breaks off.
The 172 is a lovely machine to land if flown at the right speed, those super Fowler flaps fully extended, to a correctly fully flared nose-high touchdown making full use of that sensitive elevator. Don't mess with the flaps - leave them down as Mr Cessna intended, and the aeroplane will be a pussycat to land.
As an aside, last Saturday morning two of us about to start our Concorde guide duties at Manchester were chatting when we noticed a Virgin 747-400 approaching 24R. It touched down fully-held-off, well nose high, with it being difficult to note the exact point at which the wheels took the weight - the gear just slowly contracted as more weight came off the wings and onto the wheels. The pilot kept the nose right up high, almost to the point of stopping on the runway, before it was gently lowered to the ground and the aeroplane taxyed off at the next taxyway. Beutifully done - we had both stopped chatting to watch, and it was a pleasure to witness someone really on top of their game like that.
SSD