The IRS is using the information from 2019 tax returns. Since you didn't file a 2019 tax return, the IRS won't be sending you a second stimulus check. Instead, you'll have to claim the amount you would have received as a "recovery rebate" credit on your 2020 tax return, which is due on April 15, 2021.
On your 2020 return, you will be asked about the stimulus money. You would select Yes that you did receive stimulus money, & enter the amount you received so far. Then the program will calculate if you are owed more money, or you don't qualify.
After the Other Tax Situations section of the 2020 TurboTax program you will be asked about the stimulus payment received or not received in 2020.
After you asked about the stimulus payment & you qualify, you will get the Recovery Rebate Credit (stimulus) on the 2020 federal tax return, Form 1040 Line 30.
