Q:
How can I scale my drawing?
A:
There is no direct way to do this, but you should try select all, group, then resize the whole image. With a group, everything will resize proportionately. You should hold down the Alternate key as you resize, for proportionate resizing.
The only difficulty with doing this is that when you group and resize by dragging, the text within the boxes doesn't resize, so it may get chopped off.