You cannot control the final scale, as the size/resolution of the browser or game window is controlled by the end user.
Recommend using the following settings in your project properties:
Fullscreen Mode - Letterbox Integer Scale
Sampling - Point
Pixel Rounding - On
You can control increase or decrease how much of a layout a player sees (viewport) by using the Set Canvas Size system action, but I don't think that is what you're going for...