Additionally, please use a thermometer when making his formula. The food has to be between 103-110 degrees. Any colder, and it can cause sour crop.
This is NOT directed at you, but I cringe lately when reading about so many handfeeding questions. It needs to be taught properly. Many things "can" go wrong, even if the temperature and consistency is right.
Sherry, every bird is different. If he was on 2 feedings while at the store, that doesn't mean he'll be at 2 feedings while he's with you. He's having a setback because he was taken out of his environment.
Weigh him first thing in the morning, before his first feeding. Try and keep a record of his weight, that way you know with certainty he's getting much needed nutrition.
What formula are you using? Macaws are VERY active birds, and even as babies you can add "baby food" under the formula, just a little bit, preferrably ORGANIC. Adding a bit of peanut butter is another idea..but just a tad bit.