I had unprotected sex on Feb. 17. I don't keep close track of my periods, but I know my last one ended around Feb. 2nd. Assuming it had started about a week earlier, I calculated my fertility window to be between Feb. 5-15. I don't know a whole lot about fertility windows, but I know that anytime you have unprotected sex there is a risk of becoming pregnant. I was wondering what my chances are if I had unprotected sex within a couple days of when my supposed fertility window would have ended?

If you had sex aprox. 15days after ending your period, you were most likely in your "fertile window".
A women who averages a 30 day cycle will commonly ovulate around day 10 - 16. That being said, you can't know for sure when you ovulate based on that alone. I've ovulated on day 9, 16, even day 20... each cycle is different. Also, sperm can live up to 5 days inside your body under the right conditions.

Only knowing this small amount of information, your chances of pregnancy are fairly high.