My experience with Ben Moore is that if you tell them you have used some of the paint, they don't want to try to play around with the color because they can't adjust the formula to account for the missing cup of paint.

Personally, I wouldn't worry about so little paint missing. It takes a lot of white to change a color. It will probably be undetectable to the eye. Ask them to mix it at your loss if you don't like it. You will get a creamier white even if it doesn't look like an exact match. Make a good sized swatch for scanning later, two coats for full depth of color, just in case.