does aiming for band 5 count? LOOL, but most likely if you thought the test was hard, then most people thought it was hard, thus lower raw mark required for band 6
dont forget scaling. if everyone does badly, they will scale up your mark...
another thing my teacher penalises me marks for is for a lack of structure in my essays. No doubt you have all heard of the PEEL structure, but it really comes into play in year 12.