multiply the width and height by the scale factor. If you made a variable for this, us your variable. If you are using image xscale and yscale, use those:
You can get the width and height of the sprite with the scaling using the variables "sprite_width" and "sprite_height".
If you want to get the width and height of the sprite without the scaling you can use the functions "sprite_get_width(sprite)" and "sprite_get_height(sprite)".