Exact scale matching using gumball

I have a purple curve the ends of which I want to exactly match with the ends of the red box, that is, the widths are equal. I can put gumball in one corner and then scale down using the green square but I cant get it to scale down to exactly match the other corner of the box. Do I have to redraw the purple curve?

.precise scaling problem.3dm (118.3 KB)

Hi Deborah- it is generally best to post just the objects you are asking about- in this case I see there is a purple line- is that the one? Use Scale1D snapping to the ends of the line and the end of the box edge (corner you want to match.)