You may have done quite well in your view, but these tests are normative based which means the compare the scores with the rest of the norm group.
So if you got 80% for example, which is quite well, but the rest of the group got 85%, then whilst 80% as a standalone grade is good, it's obviously not as good as the 85% comparing it to the group.
That's what these tests do, they compare you to others and that's their criteria
Hope that makes sense
Best of luck going forward