If your clock looks like it has been squeezed between a door, then you'll have to change the height or width of the clock in the backend. The default values for height and width are both 160. As most clocks are circles, this will look fine. But for some clocks (like the digital ones) this will totally mess up the clock.
To know the correct relation between the height and width, just have a look at the properties of the thumbnail in the backend.