I'm not sure which med school you've been accepted to but I can sympathize since my background is similar to yours (non-trad, 5+ years from college etc). Luckily, one of the schools I was accepted to, Tufts, has a summer program particularly for students in this situation(free of charge). Selection criteria based on your background and you're given free housing and books. The courses are diluted M1 classes along with some good study technique classes thrown in. The program starts in July( I think) and ends in August (before orientation). I'm looking forward to learning more about it but so far it sounds great for me.
I do agree with other posters not to start reading on your own since it might be a futile effort. Instead, contact your school and see if they have a similar program like the one I just described for non-trads. This will much more beneficial since you'll be taught and guided by professors who you will be seeing again very shortly.