If it's only exporting a little section of the sequence, you have probably set an in and out point on the timeline by accident. You can get rid of them by right clicking on the top bar of the timeline (just above the render color-bar) and selecting 'clear in and out' - or use the help search function to find this shortcut.
Ben
Edit Out Ltd
----------------------------
FCP Editor/Trainer/System Consultant
EVS/VT Supervisor for live broadcast
RED camera transfer/post
Independent Director/Producer
http://www.blackmagic-design.com/casestudies/detail.asp?case=therydercup