Your chances are precisely 35.65%.
…Seriously, what do you want me to say? You can never really tell what anyone’s “chances” are gonna be. Maybe something in your essays might move of the admissions staff personally and they decide they gotta admit you. Who can possibly predict something like that?
Anyway, I transferred in for math as one of my majors last year. I can tell you my stats if that would help, they were:
HS: GPA 3.4 unweighted (5.6 “weighted” from APs), SATs 2090, EC’s: nothing really honestly, just bouncing around a bunch of clubs, nothing to write about; however my HS was a “magnet” school where everyone did some kind of visual or performing arts “major” and took classes on it every day for four years, so that’s “something extra.”
Like you I felt that I “messed up” high school, so tried again as a transfer student.
I enrolled in a local 4-year private university after HS:
GPA 3.7, ~65 credits or something, all beginner/intermediate courses for math done plus some extra (I’m also double majoring in something else, those reqs were done too). ECs: vice president of a chapter of a national club relevant to one of my majors, volunteering for something that affected me personally for 2 years, visual arts, electronics/computer/programming self-learning.
For you, I think it could be hard “standing out.” Anyway, I got in with my stats. I don’t know how much that helps (hey, it could have been a long shot for me and maybe my essays were what got me in, I had very strong reasons for transferring out of my school as well as a fairly strong outline of reasons for going to Michigan specifically). I definitely don’t believe that I was a “shoo-in,” though, I will say that.
Good luck to you.
Edit: I am also OOS.
Plus, I think it’s LSA that decides to admit you, not the math department.
Edit #2: I forgot to mention some really specific stuff, like my HS is ranked top 100 in the nation, I took all the hardest courses at university, etc. It’s even harder to tell chances when lots of details like this are omitted. Also, recommendation letters.