I also had a terrible AP Chemistry teacher, so I sympathize with your plight. I think your best bet is to get a review book that can quickly fill you in on the content you didn't cover in class. Since the test is coming up soon, my recommendation is the Crash Course AP Chemistry book. It's a short book that sticks to exactly what you need to know for the exam and provides great test-taking tips. It might also be helpful to get this book of practice questions from Sterling Test Prep so that you have more ways to test yourself on the new information you learn from the Crash Course book (which itself doesn't have much in the way of practice questions).
I know you say you felt very ill-prepared after looking at old AP Chemistry exams, but I'd still recommend taking at least one timed practice test to see what happens. Even if you bomb it, you'll be able to look at your mistakes afterwards and see which topics were most problematic (and costly, points-wise) for you. You can then focus on those specific topics when you study from your review book and do practice questions. If you happen to know any older students or classmates who are chemistry whizzes, you could also ask them if they would consider helping you out with a couple tutoring sessions.
I've actually written quite a few articles on the AP Chemistry exam if you want to check those out over on our blog. In going through sample questions, I found that many of them were more reliant on your knowledge of the basic properties of different elements than on complicated calculations. It's easy to get flustered because the questions look really complex, but you might find that some of them aren't so bad if you break them down into manageable parts and write down exactly what you know and what you need to find.
Best of luck!