It would be helpful to know: a) what the schools' stats are, and b) what your other stats are before dishing out advice. You have a very solid MCAT (make no mistake about that), so to not get an interview at your school of choice makes me suspect that there may have been some other discrepancy in your app (low writing score, middling GPA, lack of research, lack of clinical experience, who knows). In terms of re-applying, schools like to see improvement in whatever area was lacking.
My honest opinion is this: before re-taking, contact an admissions officer at McMaster and get some feedback. They should be able to tell you where your weaknesses (AND strengths) lie. Don't assume that your MCAT is the only thing holding you back. While it's an important part of the process, it is NOT the end-all, be-all.
But if you're set on re-taking, go for it. There's not much advice I would give someone who has already gotten a 35. A lot of applicants here would dream of getting such a score.
I also noticed that you took the MCAT last August. Could some of this simply be related to applying late in the cycle?