October wedding

Danielle
Hi all 
Is anyone else's friends and family trying to make plans with them for September/October? 
I found out I'm pregnant on New Year's Day the doctor dated me 5 weeks so I'll be due around the 12th of September according to this app. 
Our friends get married the 1st of October we've told no one were pregnant yet and they have asked us if we want a room for the wedding because we will be traveling to it. We originally said yes but then we worked out dates and baby will only be 2/3 weeks old. I already don't want to leave it all day and over night. We've told them we've changed our mind but feel awkward because we're not telling them why. 
Any advice please?