It is very likely you have simply dropped the expander (as described by jsharr) inside the frame... turn the bike over and see if it falls out easily, or maybe take the loose bolt out of the stem and use it to try to push the expander out from the bottom. Any long thin object will do if the stem bolt does not - a straightened coathanger is one of my favourite tools for this type of job.
Also, I would love to see some pics of the bike
