Scared I'm pregnant

Hi, I'm a teenager and just last Sunday my boyfriend and I fooled around a bit. He put his finger about an inch inside me and only had pre-ejaculate on his finger. But it later occurred to me that I could still get pregnant, so I took a plan B (morning after pill) to make sure. What are the chances that I'm pregnant though? I know the morning after pill doesn't work if you've already begun ovulation. I have a 25 day-long cycle and it was day 15 in my cycle. I have not stopped worrying about it since it happened. What are the chances that I'm pregnant? When should I expect my period if I'm not pregnant? Thanks for the help.