my bitch was scanned yesterday she is nearly 6 weeks & she looks in pup. It would have been her first litter but the vet says she is not in pup or he cannot see any puppies on the scan.
Can a scan be wrong?

Scans can give false negative results, it often depends how experienced the operative is at distinguishing the shapes. At 6 weeks the foetus should be a reasonable size (from 6 weeks to term the pups grow very rapidly!) and should have been fairly easily identified, however if the bitch is carrying a small litter there is a lot of space for a small number of pups to hide! Keep your fingers crossed, she might be carrying a small litter.
Regards Al