Urgent! Can I possibly be Pregnant?

Patient: I was wondering what are the odds or getting pregnant if you never had your first period, you are almost 17, and the boy ended up cumming on the inside of your panties?My boyfriend and I were fooling around and he pulled away as he came. It got all over the inside of my underwear and a little bit on me near my vaginal opening. I waited a while to stand up but I removed my underwear and cleaned off within 3 minutes of the incident. I am worried I may be pregnant but I am not sure. I haven’t taken a home pregnancy test yet since it only happened 17 days ago as of today, January 6, 2014.I am 16 and I am fairly worried about this. I did not get the morning after pill and I am not on birth control. there was no condom involved. He was a good inch or two away and basically aimed at my underwear facing me and he missed me, but when he moved back my undies got it all over me.Also when should I use a home pregnancy test since I don’t have a missed period to go by or anything else of the sorts?Please Help, I am stressing out.