What are the chances I'd become pregnant?

My fiancé and I were having sex, without going into too much detail the condom fell off inside, not sure for how long but he did cum and this has never happened before. It was not easy to remove it but when I did there seemed to be semen inside it..  the thing is I was 2 days into my ovulation cycle. I would be over the moon happy if I was pregnant but seeing that our wedding is only 4 months away and we are in the middle of a major home renovation it would be best if I wasn't right now.. should I be concerned or since I saw semen caught inside I should be fine? It's been more then 3 days already, should I take plan b? Is it still affective at that point?