Since I still have an undergraduate record open, should I double major and work on a Biology degree increasing my GPA (cum. and science) to say a ~3.6?
I think you're looking at this backwards, as far as reasoning goes. What you need is a higher GPA, so you need to take more classes, and one way to do that is to add another major, and one major is Bio. Stop at the "take more classes" part and do some math to figure out how much coursework you need to do (at, say, a 3.7) to get your total and science GPAs to 3.6. And then you know how much coursework you need to add. Majoring in bio neither helps nor hurts you. If you love history, then do a history major and just take more upper div science too.
Would the AAMC include the BIO Degree grades into my overall and science undergraduate GPA?
Yes, undergrad is undergrad, until you have a degree.
I'm confident I can do well on the MCAT's because I am a good test taker.
Confident schmonfident. Go take a practice test for free on e-mcat.com, and you'll have some data.
Or should I just finish my Med. School Pre-Reqs and apply to a Graduate program like an SMP or Masters Science Program to up my chances for medical school.
I'd say no on masters work in lieu of more undergrad. An SMP is a last-ditch effort, and you have several more ditches. A regular masters doesn't fix your undergrad GPA, which is how they'll evaluate you against other candidates.
Would it be a good idea to retake the C+'s. I'm confident I can Ace them.
MD schools give you nothing for repeating a class. DO schools forgive the old grade on a retake. That said, C+ work in gen chem means you probably aren't ready to clobber ochem. I'd retake gen chem in summer school, or at least get tutoring, if I were in your shoes.
Don't forget that you need to have great letters of recommendation, community and medical volunteering, maybe some research, and as many interesting extra-curriculars as possible.
Best of luck to you.