I second this. I find that visualising your jump over and over again both on the ground and on the plane ride up really helps a lot because then you don't have to think about what you need to do next and you can concentrate on getting things done one by one during the jump :)
Don't be worried about messing up a jump or a few! Even in my limited time skydiving many of the people I've met had to repeat some of their AFF jumps and some needed some time in the tunnel to sort things out. Heck, we don't even have a proper tunnel here in NZ so that means an overseas trip to Sydney, Australia for us.... (looking forward to my first tunnel session at the end of the month!!!) Consider yourself lucky!
[EDIT] Oh and keep us up to date on how your next tunnel session/jump goes!