I have to add that the really important bit about this exercise is not actually getting it right in class (although that would do your ego a world of good) but being able to look over your work afterwards and spot the mistakes, then be able to identify how to correct them for next time. If you can do that (and from your above reply it seems you can
) then you are making huge steps forward and it really is just a matter of time before your photography will become something special.
HTH