You can set the width and height of the whole picture by providing them as arguments to the .PS macro, in inches. Try
.PS 6
scale only affect items that have been given an explicit size, for example circle radius 1, and also works as a divisor, not a multiplier. Eg scale=2.54 is suggested as a way to have numbers interpreted in centimetres, so radius 1 is of 1cm instead of 1inch, i.e. a lot smaller.