I'm working in Vegas 6.  I used the color curves video event fx to adjust brightness on the event.  On rendering to mpeg-2 I see that I overdid it, but when I reopened the veg, there are no fx activated for the event, so I can't tweak or undo the adjustment.  (I applied the correction to the event, not the track, I checked track fx to make sure).
I didn't do an intermediate render that would have applied the adjustments and created a new .avi
 What can I do to get back to my original uncorrected event?
If it makes a difference, this is a mutlicamera edit using Ultimate S 2, each of the camera tracks is a single long event .
Thanks.