In SpaceClaim, you create cross-sections on the Prepare tab using a library of available shapes. Then you convert a sketch line into a Beam element, assigning it the currently selected cross-section. When you open Mechanical and mesh those beams, you can display the cross-section. The default assignment is to put the centroid of the cross-section on the node. This is usually what you want, but sometimes it's not.
The image below shows two cross-sections assigned to two colinear lines. The default puts the centroid on the node, shown in green, but in this case, this is not desirable.
Select the Beam(T) under the Geometry branch and in the Details window, change the Offset from Centroid to Origin.
Now the T cross-section aligns with the Rectangle cross-section.