The tax that was withheld from your unemployment payments is not the tax on that income. It's just an advance payment towards the total tax that you will owe for the year, the same as tax withheld from your paycheck. Your tax return calculates your total tax on all of your income. Then it adds up all the tax that was withheld during the year, from paychecks, unemployment, or anywhere else. If the total tax withheld is less than your total tax for the year, you have to pay the difference.
Did you have state tax withheld from your unemployment, or only federal tax? State tax withheld would be in box 11 of your Form 1099-G.
