My girlfriend took plan b. had bleeding for 4 days after taking it. It has been 30 days since she took it she hasn't had another period yet and she took a pregnancy test 3 days ago it came out negative then one today negative also I'm still worried. Is the negative result accurate?

Its not 100% accurate no, a lot of the time HCG levels are not high enough to detect this early and its best to wait at least a weeks or two after the missed period.

Ps. I am not an obgyn but I do know this

The only 100% you will EVER get from a pregnancy test at home would be a "yes".