I would go ahead and take another test and if it is negative she is probably not pregnant.
Let me go ahead and tell you though that pulling out is not a method at all and that she can and will get pregnant doing this. There is sperm in the precum that you emit during sex way before you actually cum.
If you are not ready for pregnancy you need to wrap it up. I know accidents happen, we all make mistakes but it is more than just you and your girlfriend's life at stake. You would also be putting a possible innocent baby's life at stake.
I would also suggest going to a planned parenthood and getting on some birth control. Your parents don't have to know (I am assuming either one or both of you are underage) and they also give out free condoms.
She may just be late though. Us women do that sometimes.