I made a mistake with the stimulus screen and my return is 1200 too large. How do I amend it before getting irs return?

If you have already filed your return you will need to wait and see if your return gets accepted or rejected. 

• If your return gets rejected by the IRS, then all you have to do is make the changes on your return and refile.
• If your return gets accepted you will have to wait and see if you receive your refund that includes the additional credit. If yes then you will need to amend your return (1040X) and send the funds back to the IRS. Please see  FAQ How to amend a tax return for instructions.
   
  But the IRS has not addressed the details yet. Please see this IRS Recovery Rebate Credit for more information.

Please see the links below when Form 1040X is available:

• IRS forms availability table for TurboTax individual (personal) tax products

Thanks, I'll keep  an eye out.