The second stimulus is allowing any child that turned 17 at the last half of the year, will be eligible to receive the stimulus money. You do not have to return any money, you keep it.
From the IRS:
The IRS will use people's 2019 tax returns to determine their stimulus payments, which means that teens who hit their 17th birthday in the second half of 2020 — after tax returns were due to the IRS — could still qualify. No adult dependents will qualify for the $600 checks, according to the Tax Foundation.
No! Congress was very clear there were to be no requirement to return money,.
The way the stimulus REALLY works is EVERYTHING is based on your 2020 income, filing status and number of children under the age of 17. What these numbers were in 2018 and 2019 does not matter
The IRS will calculate your stimulus based on 2020 numbers; that is what is considered the ACTUAL.
The two payments were just ESTIMATES
if the ACTUAL is greater than the ESTIMATE, you will receive that amount as a credit on your 2020 tax return.
if the ESTIMATE is greater than the ACTUAL, (which appears to be your case) you are not required to return the money nor does it impact your refund. Line 30 on Form 1040 will be zero.
does that help?