100k is incredibly small for an audio file - that sounds more like just the .sesx file you've got. What that contains is the information about your session, and links to the location where the audio was recorded, but not the audio itself. The actual assets of the session are the sesx and the audio files, and the audio files will be considerably larger!
SteveG is almost certainly right...100k is the size of a fairly typical .sesx file but could only be a couple of seconds of sound at the most.
Just to expand on what Steve said, to save the session file and tracks in one go next time, use the File/Export/Session command and make sure the "Save copies of associated files" box is ticked in the pop up menu you'll get. You'll also be able to specify where the session is saved etc. from that menu.
As an inveterate "Save As" user it took me ages to get used to the Adobe terminology of "Exporting" things but, once you get going, it's very useful.