It can sometimes be tricky to a large widget onto another one. It can also be tricky just to move an icon into a folder as it keeps wanting to move the folder out of the way.
Exit wiggle mode, enter it again, and try again to put the widgets together. The problem with the large ones is that if you don't get it just right - as you can't fit two large widgets on one screen - it'll keep moving them around. You'll get there in the end!