I would make a note of the length of one of the edges of the properly scaled face.
Then undo the scale so everything is back to original size.
Then use the tape tool to resize everything according to the edge you measured.
You do this by clicking the tape tool at both ends of the edge, then type the size you want it to be (the one you noted earlier) and hit enter, if done correctly it will ask if you want to resize the model, say yes and everything should be scaled to that edge. (there can be issues with some geometry)