I have to agree with Brand. Aldehydes and Ketones/ Carboxylic Acids and Derivatives and Amines are inthe second semester, not to mention Electrophilic Aromatic Substitution. If you miss 2-5 questions in O.Chem, then that's the difference bewteen a 21 and 17.
I tried to take it after just O-Chem 1 and i didn't understand carbonyl groups, much less amino acids and carbohydrates. If you feel that it's easy for you and you can understand it, then just study Kaplan and totally go for it.
But again, if you miss just a couple questions on ethers, phenols, Grignards, aldol condensations, that could be the differnence between a 17 and 21. Something to think about, huh?