You can ask the Sheriff to return the writ, then get a new writ issued in the correct amount. This is good if the current writ is $800 too low. If it's $800 too high, just tell the Sheriff to collect the lesser, correct amount only, and you are all right. (Most levy instruction sheets have a space to fill in the lesser amount to collect, for whatever reason.)
If by chance the writ is $800 too high, and by a miracle the Sheriff sends you a check before you have a chance to make the correction, and the check is in the full amount (i.e., $800 too high), then you can and should send a check for the overage to the judgment debtor, along with a notarized acknowledgment of satisfaction of judgment.