SCALING OR SIZING PROBLEM

I am designing formers for an rc plane in coreldraw9.  I have created the shape and made a duplicate to shrink and put inside the original..    When I resize the duplicate by using corner handles and put it inside the original, I do not have an even distance between the two objects.  Same thing seems to happen if I use the docker for scaling.  Am I doing something wrong in using either of these two methods?