Actually the usual dosage for ROE as an antioxidant is more like 0.05% based on the weight of fats. Antioxidant dosages higher than recommended can lead to pro-oxidation, meaning the fats go rancid FASTER than if you hadn't used an antioxidant at all. Here are the results from one study I found --
"...One study looked at the antioxidant and pro-oxidant effects of ROE in soybean oil
. The researchers found ROE was ineffective at 0.01% and it was pro-oxidant at 0.5%
. They found ROE worked best as an antioxidant in the 0.02% to 0.05% range...." *
An 8% dosage is so high, I question whether I'd want to deal with that much ROE in my soap even if it was non-toxic and skin safe at that dosage. (I don't know the answer). At the very least ROE has an odd fragrance that I would think would be noticeable at 8%.
I think I'd err on the side of discarding this batch just to be on the safe side. It isn't realistic to rebatch this soap enough to cut that 8% dosage down to 0.05% -- every gram of this soap would have to be diluted in 159 grams of other soap to achieve this goal. I might keep an unused bar or two around for long-term evaluation to see if this soap does go rancid faster than expected, but purely as for info only, not for actual use.
* Hall, C., Cuppett, S. The effects of bleached and unbleached rosemary oleoresins on light-sensitized oxidation of soybean oil. J Am Oil Chem Soc
70, 477–482 (1993). https://doi.org/10.1007/BF02542579