The 20% taken out is not the actual tax. You have taxes withheld like from your paycheck. You will have to enter the whole gross original amount (before taxes were withheld) with your other income to figure out the total tax (and it may put you into a higher tax bracket) and then the withholding is subtracted from the total tax to figure your refund or tax due. The gross amount shows up on 1040 line 4a or 5a and the taxable amount on 4b or 5b. The withholding will show up on 1040 line 25b.
