I am currently a high school sophomore with a 3.8 GPA. I take the highest level English, History, Spanish, and Science classes available to me. I am one year ahead in math although others in my grade are two years ahead. I have gotten A’s in all of my classes besides math, where I consistently get a B. My history class is AP which will bring my GPA up, but Michigan will reweight it as I apply. As my math grades aren’t up to par, I am planning the next two years to continue to up my chances to get into University of Michigan Ann Arbor. I am considering taking full IB, but I am not sure if that will increase my chances enough to get into U of M. My main question is should I do Full IB, or some IB/some AP, or to apply for dual enrollment at University of Michigan Flint online, to get into University of Michigan?
I was in your same boat two years ago; I’m a senior now, stalking the U Michigan threads while I await my decision (it should be any time now). DO IB. You won’t regret it, I promise. It is extremely difficult and is much, much more prestigious than AP. There is so much more that goes into IB that you really won’t understand until you’re already almost through with it, and that’s what makes it so special. I know that one of the admissions counselors at Michigan has been quoted for saying “There’s nothing more rigorous in the United States than the full IB diploma.” Your GPA is good; keep up the grades, they will serve you well and will also give you a little wiggle room when the hell of Junior/Senior year hits. Just remember that sadness is temporary, GPA is forever 
I am terrible at math. I’ve always been bad at it; but that is not something I let bother me anymore. I try my hardest and get B’s, and so what? My skills are definitely more profound in the areas of reading and writing, and rather than be sad that my math isn’t as good, I am proud that my English skills are significantly better than the average. As long as you try your best in math and keep excelling in your other courses, I highly doubt that Michigan will downright hate you for just not naturally being good at math. It’s great that you’re already so interested; I knew of UM in sophomore year, but I never realized it would quickly become my #1 choice.
My advice as an IB senior would also be to make sure you prepare, prepare, prepare for the SAT/ACT. I only took them both twice, and I regret that because I went up so much my second time, and I am sure I can do much better a third time. Take it as many times as possible, do review sessions, study the math especially if you’re like me, and just try your best to get the highest score possible. I personally did much better on the ACT than the SAT, but it’s really whichever you like the best and you feel the most comfortable with.
Overall, IB is extremely challenging and will test your every nerve, but it will definitely pay off in the end (or so I hope, lol. I’ll update you on that once I find out my decision). I hope this was helpful; if you have any questions I would be happy to answer! 
Do you have at least a practice score for ACT or SAT? It would be hard to chance just based on your sophomore GPA. Also, try to bring up your GPA while raising your course rigor. Both are important. Your current GPA is slightly below admission average.