When printing 8X10, edited image, they are severly cropped

[irronhart]

I loaded some images onto a flash drive and went to Wal-Greens to print some 8 X 10's. When I picked them up that appeared to have been cropped about 25 or 30 % and were a lot darker. The clerk suggested my file may be too large. Can anyone explain what heppened here? Would I be better off using a service such as Adarama or Snapfish?
Any help would be much appreciated.
irronhart

[dj_paige]

Your images must be cropped to an 8x10 aspect ratio before you print them. You can do this in PSE, or you may be able to do this at the store.

I don't know why they were darker, there are a dozen possible reasons.