I've played through this quite a few times and the 1/8th timing does seem to be right. When I play through a couple times my average is only 3ms late.
When you slow it down to 25% and look at it, a lot of the lyrics best fit on 1/8th (Especially during the first third of what you've mapped so far.) so I don't think there's anything wrong with what you've got, the song's just a little deviating at some points it would seem.
I say you should just go ahead and map the rest of it, but that's just me, and what do I know honestly? x_x;
Edit : Failure.
When you slow it down to 25% and look at it, a lot of the lyrics best fit on 1/8th (Especially during the first third of what you've mapped so far.) so I don't think there's anything wrong with what you've got, the song's just a little deviating at some points it would seem.
I say you should just go ahead and map the rest of it, but that's just me, and what do I know honestly? x_x;
Edit : Failure.