Export file much larger than contents

Usually that happens when there is a stray clip as small as a single frame stuck out on the time line somewhere.  Sometimes it will even be on another track.   Pressing the "/" key will fit the project to the visible timeline.  If your project shows up in the left portion, there is something out on the end somewhere.  Use your mouse to hightlight everything to the right of your project and press delete.  

Another workaround is to use the "work area bars" and check the work area bar only box at output.