Does the IRS website indicate that you were sent less than what was reported on your federal tax return Form 1040 Line 34? - https://www.irs.gov/refunds
If so, you will need to wait for the IRS to send you a letter which will have the changes the IRS made to the return which changed the refund. If you disagree with the IRS there will be a procedure in the letter to dispute the IRS changes.
