This must be another example of what I call "Dark Shadows time." They aren't explicit about when there's a change of day - but, Morgan wanted to marry Catherine immediately after his father's death. I think it got postponed one day. Then, when they tried to do it, Bramwell intervened - another day. They had to hold the lottery, so that was at most the next day.
It seemed to take a day to get Gabriel into the room. Then, after his experience, they learned that they had to hold the lottery again. One has to assume it's been at most a couple of days since then.
Somehow Bramwell completely recovered from his wound in a day or two!
Meanwhile, even if we expand this time a bit and say that it's been 2 -3 weeks instead of the 1 week it would seem to be, there's still no way that Catherine would know she's expecting at this point!!!