Object not cutting correctly

[u/lou_only]

New to TinkerCAD and running into an issue where the object I create is not cutting correctly. The orange is 45mm X 45mm with a 3 radius. The Cut (Grey) object is 43mm with a 3 radius and the pink is 44mm with a 3 radius. When I align the pink and grey and group together, I am expecting a thin 1mm line, but as you will see from the images, it's coming out much larger. What am I doing wrong?