You should not be having this much anxiety from doing sexual acts. I would recommend that you stay away from these types of activities until you feel ready.
Is this before or after you had sex and took Plan B. Basically, your chances are none. I do suggest you consider abstaining though. You are still concerned about pregnancy despite numerous people saying it's pretty likely you're not and that alone shows you're not ready for the consequences that come with sexual activity and intercourse. If you don't want to be pregnant, don't take the risks.