Hi there
I took the test last year, and studied for about 3 weeks and did fine (I am also a psych major though). I would heavily recommend purchasing a Kaplan or Princeton book (I used princeton). They will focus in on the key people/theories to remember. In the Princeton book there is also a practice test that breaks down the questions by area (e.g. developmental, sensation,etc.) That will allow you to realize which areas you are weak in and focus your studying on those areas.
Also...remember that not all schools require the psych GRE....so if you don't do as well as you expect don't stress out too much 🙂