Keep in mind that you are not a HSC marker, and when they mark, it is not just a case of right or wrong, you get partial marks for working and demonstrating that you understand concepts. When I did the HSC in 2002 I did maybe half the paper and ended up with a mark of 87. Keep practicing and...
I'm not sure how you figure general math and 4u scale the same? If you do 4u you get an assumed band 6 for 2u, plus a quick look at the 2007 scaling table someone else linked to (http://www.uac.edu.au/pubs/pdf/2007_table_A3.pdf)will show you that one is scaled down (a lot) and the other is...