All I know is that a test can say that you're NOT pregnant even when you are, however, it can't say that you ARE pregnant if you're not. This is because the test cannot pick up the "pregnancy hormone" if it's not present in your urine, but it could possibly miss it (giving you a negative reading, even when you are pregnant). So if it read positive, it definitely picked up the pregnancy hormone -- thus, meaning pregnancy. Go to the doctor and get a blood test if you want to be 100% sure, but unless there's some flaw in the product, I'd say that you're pregnant.
Good luck w/ everything.