I suggest searching for the previous version of the file on the usb stick as well as in the temp directory of windows. If you used MS Office you should have a copy in the same folder for autorecovery.
Which office did you use? 2003 or 2007 or previous versions.
Where is the computer you used to do this? (school, library, home?)
There are tools available to recover files from hard disk as well as your usb drive
some of the best solutions can be found
here (click on me=)
Regards, Cyber.