Fix number of bins
The number of X bins of TH2F should be the same with the number of X bins. [1]
The current version is set to the number of bins of Y axis.
This will not make any error but I would like to fix it.
[1] https://root.cern.ch/doc/master/classTH2F.html#a7754fef4bcd5079d8207417a7659629e