Also, I live with my parents and they will seriously kill me if I postpone again.
If they're rational, they'll understand.
Or they won't. Doesn't particularly matter, because this is about you and your future, and your knowledge regarding the LSAT and applying to law school far surpasses theirs. You need to do what is best for you. (You might try explaining it to them in terms of tuition and employment rates. Sometimes the hard numbers help.)
Do you want to take this test on Saturday? You've already said that you feel underprepared, but, do you actually want to go take it? Do you feel like there is a strong chance that it will work out the way you want it to?
If your answer is no, postpone and don't doubt yourself for a minute. Promise yourself that you will score at or close to 170 in December, and do everything you need to do to get there.
At the very least, if you go into that test feeling insecure, you are bound to do worse than if you went in feeling confident about your abilities. And you should not short change yourself those purely psychological points.