The results of your test vary greatly on how much and how often you've used it, in close relation to your body weight, but - on average - marijuana can only be detected for up to a few hours in the blood and up to 2 weeks in the urine. Heavy users, however, have often tested positive for THC even 90 days after their last use.
At this point, it's more important to consider your unborn child's health than worry about whether or not you'll fail this test. You should let your doctor know that you've been using so that the proper measures can be taken to ensure the safety of your baby.
Id be willing to put money on it that you'd come up negative.