My girl should be day 62 from 1st mating.  After advice on here I had the vet scan her who said he only seen 1 puppy.  Since then she has remained a bit swollen at her vulva, breasts have filled a bit, but thats it.  No weight gain, no belly and I cant feel a thing in there (sat for hours with hands on her side)  I am now thinking he got it wrong, should she be looking fatter with one puppy? should she still be going through the panting and digging etc?

I think it depends of the size of your breed if you would "see" one puppy.

With just one puppy, she might not start giving birth naturally (something to do with the hormones released) so I think you will need to go to the vets to make sure there are no issues.
She might have carried a pup and the pup might have been absorbed so there might not be a puppy there anymore, even if there was one at the time she got scanned. But to be on a safe side, if one was seen in a scan, I would get her checked out soon.

I have a breed that often don't look noticeably pregnant if they're maidens.  And I had one in particular where the pup didn't move down from under the ribcage until the day before she whelped, so I would never have felt that one.  :-)

She's not a maiden, this is her 2nd litter. She is a fairly large breed but I'm just not convinced.  I dearly hope she is though.

I have a large breed and people didn't know she was pregnant just before she whelped and the vet said she was only having a small litter (no scan though) and she had eleven good sized pups. I am positive that had she been having 5 no one including the vet would have known! (Without scanning). She obviously hides them well.

It's usually pups becoming uncomfortable space wise that induces the release of hormones which starts labour off so I'd agree this might mean labour starts later with one pup if at all so I would keep the vet informed.

If you want to know if she has any/one then I would ask your vet for a conscious xray - you just need one pic of her and any bones in the pup/s would be visable for a head count