Questionable X chromosome?

I’m 21+4 and I have an appointment tomorrow for another anatomy scan and I’m so worried bc I already had the anatomy scan at 20 weeks and then my doctor called me and said there was something questionable about one of the X chromosomes and said he made me an appointment at the hospital he works at (and I normally would go to the place down the street from me where he also works) we did find out it’s a girl but idk what he could mean by something questionable about one of the X chromosomes Is he saying something is wrong and they just don’t know what it is yet or what like how can it be something questionable 😭