Savina
If you didn't have sex and you didn't "come" anywhere near her v****a, then she is either cheating on you or not pregnant.
Stressing out about being pregnant can make your period late as well.
Agreed. You did not give us much to go on here, but it's rare to get pregnant without having sex. It is possible if ejaculate or pre-ejaculate gets close to her v****a, but it is not all that likely. It is difficult to tell you any specifics without knowing exactly what you two did.
Stress and many other things can cause a period to be late. Also, being three days late isn't really a big deal for most women. When women predict when they should get their next period, it is usually give or take a couple of days. Irregular periods are very common, especially among teens.
In the future, be careful. Maybe look into protection now even if you aren't having sex just yet so that you will both be ready when you do.