Well, there are two types of scaling this. One would be as you have done with the Tie points (and that is what I instructed you to do, so correct.) the second one is to use ground control points measured with an accurate GPS, which is a bit harder and more expensive solution. What I would recommend is to get a large meter and do the measurements on it as it is very accurate if it is for the construction purposes. You now are doing it by a side of a house which you have probably measured, that might be quite inaccurate so I would not expect it to be perfect.