I'm not sure if I understand your question correctly, are you unable to get the drum cap back on? If so see my first paragraph.
Take a look at this article from
4x4wire.com. What you need to do is turn the star wheel back down, because the brakes self-adjust between each time you apply them from forward and reverse directions. The star wheel part is in this
picture. With new shoes, the thickness is more than that of your old/worned shoes causing the drums not being able to fit over them. You're trying to accomplish the same thing as compressing/clamping back down the caliper piston on a disc brake setup.
If you got the drum cap back on, try adjusting the star wheel so that it pushes the shoes out far enough so that you feel some drag and resistance when reinstalling the drum cap.