That is a very low reading score, compared to all of the other sections, especially your writing score. It's curious that you scored so low... are you sure you weren't just having a bay?
If you are really a 13 in reading, you might want to work with some "non TOEFL" sources to practice your reading. Grab some graded readers, perhaps scan National Geographic and buy a vocabulary textbook.
And, of course, keep doing practice tests. There is a new "Complete Idiot's Guide to the TOEFL" which was just published and has a bunch new practice tests. And it is much cheaper than all of the other books.
:TOEFLresources.com: Step-by-step guides to the test and a free essay evaluation service