Note that PA schools usually require somewhat different prereqs than med school. For example, one PA school I looked into requires Psychology.
Anyway, a basic science BA/BS is really useless. You'd probably want to keep PA school, MS programs, PhD programs, or a BSN-conversion program in mind if you fail to get into medical school. One really interesting option I haven't explored is Pathologist's Assistant (only 8 programs in the US, Master's level)--they do all procedures that Pathologists can do, except interpretation, and starting salary is $75,000 with high demand and most graduates get a job offer before finishing school.
Don't forget PharmD, DPM, and Dental school.