Weird. This question was posed a year ago and it seems you have posted a duplicate. Help us understand.
I am not sure why you tested if you haven't had sex. That's really required for pregnancy. If you leave a pregnancy urine stick sitting, it will develop a second line which is just the evaporation line and does not mean you are pregnant. I agree with ppowb. :>)
You can’t be pregnant without getting sperm in your vagina. Maybe you were reading an evaporation line some time after taking the test. Maybe something happened at that party you did not notice. Maybe the test was faulty. Do you have any early pregnancy signs? Wait a week and run another test.