You can take both pills at the same time and it will not change how effective it is.
I also want to tell you that you did the smart thing, and because of how early you took it, it's likely that it worked.
I just want to warn you though, that you may have some crazy periods for up to three months. If your period is late, don't worry until
after you've taken a pregnancy test. Sometimes Plan b can make your period come early or late and it can be really heavy or really light-- totally normal.
If you're not comfortable with what happens, then always test first.