I felt that I was pretty ready for the September LSAT. I took a prep class with Kaplan, took the two days off of work before the test, had a good night's rest the night before and got to the testing location on time. So I get seated and finish all of the stuff that you have to do the test. The proctor tells us to begin on section 1, so we all do. About three minutes into the test, one of the proctors comes up to me and lets me know that I am working on section 2! I was mortified and freaked out. Because I was so used to taking Kaplan's tests, I was used to flipping past the first few pages of instructions and such. However, the real LSAT doesn't have instructions, it just goes directly into section 1. This ruined the rest of the test because I couldn't let go of what I had done. I was convinced that I was going to have to retake the LSAT, but decided not to cancel my score.
In the end I scored 4 points higher than I had on any diagnostic test I took. So it worked out fine, but this experience was awful.