If that is the only time you had sex, and you have a very predictable cycle, I would not be worried about pregnancy. In order for you to sustain a pregnancy, your luteal phase (the days between ovulation and menstruation) needs to be at least 10 days long. If the average woman has a cycle of 28-days and ovulates around day 14, she has a 14 day luteal phase. You, on the other hand have a very short cycle which means there is a good chance that you have a luteal phase defect which may prevent you from having children if you don't have it corrected.
To understand when you ovulate and to determine if you have a sufficient luteal phase for pregnancy, you should try charting your cycles for about 3 months.
you would have ovulated before the time you indicated you had sex, so i think it's unlikely you're pregnant, but i guess you never know. a million and one things can cause a delay in period, like stress, etc. :)
What I was saying is, if you had only 2 days before your period, that isn't enough time for implantation to take place. In order for you to sustain a pregnancy, the fertilised egg needs about 10 days before it implants into your uterus. If you are trying to get pregnant again, you may have some difficulty with such a short luteal phase.
I agree that you should not be fertile during that time. However, I had cycles of 21 days since I first started my periods as an 11 year old. I have 2 children and got pregnant the first month with both, fortunately and without opk's. No probs there for me. I conceived on cd 9, 10, or 11. Three day window. Don't stress about it. Wait a week and if af doesn't come, then retest-first voiding of the day. I hope everything turns out ok for you. Best wishes.