Why does box 1 of my 1099-G state that I received more unemployment compensation than I actually did?

Did you have taxes withheld from it?  Just like with a W-2, you are taxed on the gross amount, not the amount that ended up in your pocket.  But the program gives you credit for those withholdings.  However, if you think it's still wrong, contact your state unemployment bureau.

Just to supplement SweetieJean's answer, the IRS is providing the following advice: 

Taxpayers who receive an incorrect Form 1099-G for unemployment benefits they did not receive should contact the issuing state agency to request a revised Form 1099-G showing they did not receive these benefits. Taxpayers who are unable to obtain a timely, corrected form from states should still file an accurate tax return, reporting only the income they received.

Please see Incorrect Form 1099-G for unemployment benefits on the IRS's Double-check for missing or incorrect Forms W-2, 1099 before filing taxes page for more information.