Normalizing a Gaussian Distribution

Histogram will show you the number of samples in each bucket. Since your sample size and number of buckets didn't change the values in histogram will stay the same. You can scale the number of bins to get closer to the graph you're expecting.

Note that it will still be discrete bars. To get a smooth curve you can use kernel density smoothing technique.

The Histogram doesn't how densities but partial cumulative distributions over intervals [A, B). Mathematica has an option to translate into densities and normalize different graphs.