this is from IRS website
Tax filers with adjusted gross income up to $75,000 for individuals and up to $150,000 for married couples filing joint returns will receive the full payment. For filers with income above those amounts, the payment amount is reduced by $5 for each $100 above the $75,000/$150,000 thresholds. Single filers with income exceeding $99,000 and $198,000 for joint filers with no children are not eligible. Social Security recipients and railroad retirees who are otherwise not required to file a tax return are also eligible and will not be required to file a return.
Eligible taxpayers who filed tax returns for either 2019 or 2018 will automatically receive an economic impact payment of up to $1,200 for individuals or $2,400 for married couples and up to $500 for each qualifying child
so you should get the $3400. but you can wait so the IRS uses the 2018 return. the actual credit will be calculated using the 2020 return. so unless you remarry you would probably file as Head of household with 2 dependents so you would be entitled to only $2200. against this the advance payment would be subtrcted. so you might think you would need to pay back the extra $1200. at the present time the law contains no provision for any excess to be repaid or included in income.
