Results from Teas Differ from practice tests.

OK so I took the TEAS V exam at my school. My score was 68%, 71.4 % on the Reading, 60% on Math, 75% on the science and 60% on the English. However, I just took the practice exam on ATI's website and my score was 80% on the Reading, 70% on the Math, 54% on the Science!! and 66.7% on the English. On the actual exam my strongest area was the science and on the practice it is the weakest?? What gives? Should I be worried?? I retake the Teas in 2 weeks!!!