Are you sure that the number is incomplete, and it is not just being rounded when it is being displayed?
Try an expression of sum(Number) * 1000000 and see if the further decimals are actually present and just not shown.
When you come to display your numbers, if you need all those significant figures, you can provide a Custom number mask and provide the number of decimals you need, as sasiparupudi1 suggests.
If the number truly isn't loading, then you could create another sheet in Excel which has those values multiplied up (e.g. =A2*1000000) and then try loading from there instead.
Hope that helps!