You will need to figure out why you aren't getting the full amount before you go trying to adjust the credit.
Is there enough of a tax liability to take the full $2000?
Does the child have a valid SSN for work?
Is the information worksheet information entered correctly? Are you using Code L (dependent child)? Is the NOT qual for child tax credit check box "X"'d or empty?
We will need a little more info to help diagnose the problem.