You bought pre-cuts instead of 96" length 2x4's. Pre cuts when assembled with a double top plate and a single bottom plate will be a little over 8 ft. So an 8 ft piece of drywall will fit perfectly without touching the floor. Ditto if drywall is installed horizontally since it is exactly 4 ft wide. That is why they make precuts. I once got some by mistake not paying attention to labeling and the fact that for some reason the store had two stacks of precuts, and they were not near each other, so I made an assumption that since they were next to the 10 ft ones, they must be the 8 ft ones. Wrong, and the 8 ft ones were some place entirely unrelated, with 2x6's. Caught it when loading into back of truck when I noticed ends of boards too far from tailgate. I got off lucky there catching it in the loading zone. LOL. My wife was with me too, and she got a good laugh at my expense.