Based on the info provided, there could be a couple of possibilities happening here:
- More than one copy of X-Plane 10 installed on the machine. Scenery may be in Copy B but you launched Copy A.
- You may be assuming the accuracy of the little boxes on the installer map where you select scenery is better than it is. You could have picked ONE TILE only, but the airport being loaded may be slightly off that tile onto an adjacent one. Try re-installing tiles for an entire region - not just one or two.