1st Stimulus Check

The 1st stimulus check was based off of 2019 taxes since 2020 taxes could not be filed yet. However, if 2019 had not yet been filed then 2018 return was used. Correct?

My 2019 taxes were not  yet filed & my 2018 AGI was used which gave me a lesser amount than the $1200 ($2400 MFJ). Once my 2019 taxes were filed, I was well below the AGI to receive full amount. 

My understanding is when I filed 2020 taxes I could recoup the difference in credit on my taxes, yet TurboTax is using my 2020 AGI (increased again) and says my stimulus received is correct and no credit is due.

Is this right? Doesn't seem so to me. Thanks!