OK ... BOTH stimulus payments were an ADVANCE on the 2020 credit. They used the 2018 or 2019 info to estimate your credit in advance however the credit is reconciled on the 2020 return using the 2020 info which may or may not be good for you. If you did not get enough in advance then you get more on the 2020 return. If you got too much in advance then you get to keep the excess ... there are no "take backs".
Read up here : https://www.irs.gov/newsroom/recovery-rebate-credit
