In my opinion it's really no big deal. I also had a 4.5, so naturally I was very worried myself. But *every* prof with whom I raised the matter told me it was nothing to worry about. They were right: out of 13 applications, I got in at 7 schools (including a top-5 school, and all the others but one were top-25) and got waitlisted at two more (including NYU--obviously, that didn't amount to anything). During my visits, when I discussed my initial fears with profs who had been on the admissions committee, they again unanimously confirmed that, in general, they pay the AWA score *zero* attention. Now, I suppose it could play against you if your other scores are low, but unless that's your case, my advice would be not to bother re-taking the test. They won't look at your GRE scores again after the initial screening, anyway. Better to concentrate on your writing sample.
Hope that helps!