Next time you need to hang a wall grouping (or even if it's just one picture), here is how to accomplish your goal without stressing out!
Lay out your gallery arrangement. Flip frames over. Mark hanger/nail spot on several pieces of wax paper taped together. Flip waxed paper over, tape to wall, nail into wall where indicated. Remove waxed paper. Hang photos! It's THAT simple!! (Now, again, I cannot take credit for this brilliant idea... I discovered it through Pinterest. It is from a blog called Roost. So if you would like to check out the photo, you can find it there.