I still come up with a total of 77 sts. There are 4 left after the last M1. Are you trying to have the same number of sts between all increases? I don't think that's possible but depending on your pattern you might use 6 sts between M1s in 2 or 3 places, increasing the last set of 4 sts to 6 or 7. I'm probably not even addressing your concern though. Someone will have an idea for you.
ETA: What is it you're making? Can you link to the pattern?
I should never overestimate my basic arithmetic skills.