We would be guessing unless you tell us bit more about your Project settings, your source media and your export settings.
My guess... nothing matches.
The sequence setting are 1280 x 720, 59.94 fps, square pixels and the source media is the same...
Is there somewhere I can check the render settings?
All I found was Video Previews under sequence settings. The file format is set to Microsoft AVI, and the Codec is DV (24p Advanced)....
Your "DV" preview codec is wrong for the footage and the sequence setting. This is probably your issue.
DV is 720 x480. Compare that with your source footage
Thank you for taking the time to answer a newbie's question . Everything's back on track.