RUDAS
IMHO, the 172 is a very underrated flying machine, it has a very effective wing that generates loads of lift and must be flown at the right speed "over the numbers."
I wouldn't b*gger about with the flaps if I were you, but I might consider ASI position error.
What speed does the book say you should approach at? If you are flaring enthusiastically, could your ASI be under reading? Are you flyig solo or one up?
Sounds to me as if a few circuits with an instructor could be helpful, really get to grips with the beast.
Although most of my hours have been on PA28, I have about 30 on 172s, from the F model to the P (not the R though) and that lovely wing keeps producing lift down to about 30kts
