This may be to additional TurboTax fees, refund offset, or if the IRS made a correction to your tax return resulting in a lower refund.
To see a breakdown of your charges follow the directions in the following TurboTax FAQ.
If it is due to a refund offset or the IRS making a correction to your return, you should soon receive a letter from the government explaining why you didn't get the entire refund.
Here is more information on refund offsets.
You can also contact the Bureau of Fiscal Services at 800-304-3107 to inquire about a possible offset.