Ditto to Sarris and Alan's comments. The LOOK in the U-turn works (at least for me as well, I didn't get it at first). We had many first time riders who went outside the box on the U-turn but still passed.
The biggest thing for me was nerves. I was doing fine ("thumbs up" and "you got it!") from the instructors, but when it came to "test time", nerves kicked in, and I barely passed. Just remember to breathe and keep calm, you'll do just fine.
I'm still practicing !!