The spotting is likely the result of taking Plan B. It is a very common side effect.
It is unlikely you would get pregnant having sex so close to when your period was due. Your fertility would be near its lowest point.
A late period is also a common side effect of Plan B.
It is not a good idea to have taken Plan B twice within a cycle. They contain very large doses of hormones. Your next SEVERAL periods may be early or late and heavier or lighter than normal.
Thank you so much for your reply medic-dan :)