I too was wondering about what exactly they include in the science GPA.. Like human anatomy?
As for the other question regarding taking a core class over the summer at a different school.. I would not recommend doing this. I've seen on many med school web sights that they don't recommend taking many core pre requisites outside of your major undergrad school.. Especially if you haven't done well in some of them already, your best option is to take them in your main college and do well to show that you can handle the coursework.