Being on your period does not "greatly improve your chances" of getting pregnant. It's possible to get pregnant while on your period, but there's nothing about a period that makes pregnancy more likely to happen.
If your period was due Friday, wouldn't next Friday make your period a week late, not 2? If it was due last Friday, your period is only 5 days late. That's not uncommon for a teenage girl. Your body is still changing and adapting, and hormones can easily affect a period and cause a delay. A negative pregnancy test makes me think that your period is just late.
Give it another week and then test again if your period doesn't show. And please keep us updated, hon.