Hi and welcome to Just Answer!
You do not need to amend your 1040 tax return.
The gift tax return is a separate tax return. If you were required to file the gift tax return - simply do that now.
Here are forms - http://www.irs.gov/pub/irs-pdf/f709.pdf
Do not forget to sign the return. Do not file with your 1040 form - there is a different address for the gift tax return. File Form 709 at the following address -
Department of the Treasury
Internal Revenue Service Center
Cincinnati, OH 45999
See instructions for more details - http://www.irs.gov/pub/irs-pdf/i709.pdf