I just measured it and took a taste test.
At the same time I bought the kit a second time and did it right the second time.
Despite the error, both have roughly the same OG and current FG (not the official FG yet though). From sampling the uncarbonated flat beer, I think I actually like the one I screwed up better and decided against adding in more water.
I might change my mind once its bottled and carbonated, but I don't think, other than losing a quarter of my beer, overboiling it did that much harm.