I caught my error before IRS paid my refund
You should never amend a return until the originally e-filed and accepted return has been processed by the IRS. Most likely, you will still receive the original refund. If so, you'll have to turn around and send back the over-payment to the IRS.
What I would suggest, is that if you have not received your original refund by Apr 15th, you go ahead and pay the amount on the amended return. You can do that online at www.irs.gov/payments.
Otherwise, if the IRS sends you only the amount on the amended return (highly unlikely, but not impossible) then you do nothing.
