If that's the case, then the really is no reason to push your body to its physical limits by trying to drive back from Vegas in just 2 days. Being young does not may your body more able to handle fatigue, and frankly, no one is "built for" being on the road 12+ hours a day. Being young only means you are less likely to pay attention to the danger signs, and you'r brain will let you "think" you're just fine, even when you should not be on the road.
Take 2 and a half days for the drive back. It will be much safer, much easier on your body, and you'll still have most of the day back at home to rest and recover.