yes, but at the same time, someone with high numbers but no interesting life experiences will fare much, much better in the med school application process than someone who's accomplished a lot outside the classroom but has low stats. unfortunately that's just how it is--it's still a very numbers-driven process, although i wouldn't go so far as to say that 'med schools *only* look at numbers'. however, many schools do indeed use GPA/MCATs for initial screenings and no one will ever get to see what else you may have accomplished unless you have the stats to make the first cuts. it's only later that the app really gets scrutinized.
lily, having a competitive science GPA is very important, so definitely work on bringing that up. take a few years beyond college to work on that if you have to. and no one will care if you take the classes over the summer, as long as they are science courses and you do well--that's the bottom line. being a teacher definitely won't hurt you in the app process--provided that your numbers are competitive--and may even give you something interesting to talk about in interviews.
good luck to you!