I started my period on the 10th of September and I was supposed to ovulate on the 25th, according to an ovulation calendar. I had unprotected sex for only about five seconds on the 27th. My boyfriend did not ejaculate inside of me, but he came on my chest and then I washed it off in the water (we were in a hot tub during all of this). I know that ovulation calendars aren't 100% accurate, so I took Plan B One-Step about 17 hours after this all happened, even though it was supposedly after I'd ovulated. I'm concerned that I could be pregnant from pre- or the semen within the water in the hot tub. I'm really stressing about it. What are the odds that I could be pregnant? Should I be worried?