I tried the diagnostic last night, and I couldn’t even finish, I gave up, tired and frustrated. I took Principles of Chem I and II but there seems to be some organic chemistry and some other really specific stuff that I didn’t memorize (like the names of each theory, and freezing/ boiling points). I feel very disappointed and have lost faith that I will do well on the actual test. Is this how the real test is? Is it okay that I skipped the rest of the diagnostic and went on to the content? Will I do okay if I just read the content/material review sections?
Well it is hard ! no doubt , you just have to show Patience 
spot out ur mistakes and work on them , u can score amazing , Iam giving SAT II on coming 5th , Biology Chemistry and Physics , but the problem is XD i have old edition books XD can anyone help me by sending practice tests? of the new editioned books* ?
Barrons is good to study from, but get the official guide with 4 real tests to see where you are really at.
How does the content for the SAT Subject test compare to AP Chem content?