No it doesn't! Cream rises to the top! Hence the saying top off the milk.

Do I really have to spell everything out for you this week?
You refer to
manky (bad) cream.
I made a play on this theme, from a wicked agricultural perspective, of selling manky cream by hiding it below
good (non-manky) milk.
You are perfectly correct in your assertion, no doubt gleaned from the "Bunty Domestic Science Annual", that cream is indeed less dense than milk and will thus float on its surface, irrespective of the degree of mankiness.
I am sending you the large box of Swiss chocolates that you will be craving.
filled with Evening Primrose oil and Nytol.