I am sorry about losing your husband, if your husband died in 2019, you can still file a joint return, allowing you the Married Filing Joint tax breaks. If your return is rejected because of your 2018 AGI, I encourage you to change your filing status from Single to Joint, and use your 2018 AGI from your joint return.
In 2019 your filing status should have been Married Filing Joint. For the next two years (2020 & 2021) your filing status should be Qualifying Widower provided you meet these requirements:
- You haven't remarried,
- You have a dependent child that lived with you all year,
- You have paid your own maintenance costs of your home, and
- You have been able to file jointly in the year of your husband's death.
For more information see IRS Publication 17, page 23.