Sorry for answering late; if you're still having issues with the kata, false positives and false negatives are numbers that are not multiple of 3 but reported as such (false positives), or, numbers that are indeed multiples of 3 but not reported as such (false negatives).

Either way, if you're having issues with those, consider making a loop within a range i.e. 1 to 1000, and for each one of them (let's call them i), convert it to binary, and make sure that is recognized by the regex only if it's multiple of 3 (i % 3 == 0), nothing more, nothing less.
You might discover that maybe some numbers are falsely reported, or are missed when they should have been reported - a.k.a false positives and false negatives.