As per its documented Syntax it is easy to use the Create Fishnet tool to create a fishnet of 80 label points by making:
number_rows * number_columns = 80
However, also as per its documented Syntax, there is no option to provide a clipping/selecting polygon that restricts creation of label points within its boundary.
As a workaround you could decrease/increase the distance(s) between fishnet points until, when clipped with your polygon, they number exactly 80. To automate that process would require using ArcPy (with a
for loop) or a ModelBuilder model (with an iterator).