Plan B - I had unprotected sex from Sunday evening and took the morning after pill Wednesday morning

Yes, you could be pregnant. The Manufacturer of Plan B state on their website that you are not covered for any episodes of sex that happen once you have taken the drug.

As it was, you were only around 75% covered for the sex you had on the Sunday, because of how late you left it to take the Drug.

As we are now outside the 5 days timescale during which you could use other emergency contraception, it's just going to be a case of waiting to see if you miss your next period, & doing a pregnancy test if you do.