Making quality better that would be a nice trick
I'm affraid that can't be done. This happend to me too once. Recorded for weeks on half size for nothing. It's mistakes like this where you learn best from
If you record on fullsize and in vegas you do your resolution /2 and your bitrate up a bit maybe like 4000 or 5000 (depending on how big you want your file to be mostly) then your quality should be pretty good.