
Unless the person doing the ultrasound specialises in the equipments use, the number of pups seen is no indication of numbers likely to be born.
I was once told they could see 3 and 8 were bortn (though 1 died) and when a speicalist in ultrasound did my bitch at only 25 days, he thought she would have an average litter of 5 to 7, and we had 9.
I tend to rely on Ultrasound to tell me that there isn't just one large pup, and to confirm pregnancy.
When did you increase her food? Normally I don;t give any extra until I know they are pregnant for sure, and n9ot before 5 weeks. I then give an ounce extra for each week, so by whelping they are on half as much again as normal.
After whelping, mine at any rate are on four times their normqal diet from about the second day. when pups are almost fully weaned it starts to reduce from about 5 weeks. By the time the pups leave the bitch is on normal rations or a bit more depending on how her condition has been maintained.
Keep the quality of the food high, and don't be tempted to start any needed reduction diet until after the post partum full moutl that bitches go through. this can drag them down, so that there is no need to reduce their food below normal, as excess weight will be burnt off repairing the body and coat. If they are not carrying extra weight, then a little more food than normal may be needed until the bitch is back in coat.