Now I am getting same integral changing the bin numbers. However the maximum counts in the histogram changes after changing binning value e.g for 180 binning, max count is 1200 and for 1800 binning, maximum count is 150. Is it expected?

Yes it is expected, since the smaller is the is the bin, the smaller is the number of event falling in each bin.

As very rough of estimation if your bin width goes down by a factor ~10 you should expect also the counts of the maximum bin to goes down by a factor ~10.