It is definitely possible to do well on the physical sciences section if you are weak at physics, but you must have ample time to bring up your score, and you must be persistent and work very hard.
First you need to determine if you have a weak physics background because your math skills aren't the greatest, or because you didn't learn the material as well as you hoped in class. Perhaps you didn't learn the material as well as you hoped because your math skills are not the greatest? I am by no means attempting to conjecture at your mathematical abilities, all I want to say is: you need to determine why you're not happy with your physics knowledge. Studying all the physics in the world isn't going to help as much if you don't attack a potential weakness in math.
Make sure you can do arithmetic quickly, are comfortable with doing long division, or know shortcuts to obtaining the answer , such as fractions, etc. Be comfortable with dividing decimals. Be very comfortable with scientific notation, and how to manipulate scientific notation.
Now, you may have to learn some physics for the first time, instead of reviewing it. To do this I recommend the following : Start with Nova physics, read the entire book, do all the problems. Then buy the Berkley Review books for physics, read all of them, do all the problems. Finally, get a copy of the Princeton Review science workbook and do all of those problems. This is what I am in the process of doing, and my physical sciences score is going up. Nova Physics and TBR are really good at teaching concepts. TBR problems are very difficult, so don't be frustrated. You can do well, granted you do A LOT of practice problems. Physics is learned through doing problems, through practice, and through repetition. It requires a good deal of time, perhaps three months before your test date.
You should also work on your test taking strategy, by eliminating wrong answer that are not in the range of the correct answer, have the wrong units, or are the inverse of the correct answer.
Also, have of the battle is in the chemistry, so I would recommend doing the same for chemistry as you do for physics.
