I think she is not pregnant.
Only read a pregnancy test within the prescribed time period. Evaporation lines hours later do not count.
Stress can do it, for one.
Sweetheart, if you are this freaked about fatherhood, use condoms along with the birth-control pills she is taking. It's a good habit to be in anyway, because it reduces the exposure to STDs,
(I'm glad her period came, but it really did sound like you were worried for nothing.)