Step 5: Put it all together
To wrap it all up, put all the dice together around the steel ball and try rotating it a few times. It should rotate fairly freely. You may be able to ease the action a bit by applying silicone spray or "cube lube" to the internal faces, magnets, and steel ball.
If it doesn't seem to want to stay squared up without all the pieces in, don't worry; once all the pieces are in place, it should square up all by itself.
2x2 cubies are usually a bit more than 3/4" if I remember correctly, so the 2x2 dicecube is going to feel a little small, but not uncomfortably so.
Now go make some 2x2 cubes and tell me about your experiences!