@bhmayton - the responses presume you file a tax return for 2020. I kinda got the sense from your question that you were a 'non-filer' in 2018-2019 (where did you enter your information? it was otherwise automatically calculated by the IRS from your 2018 or 2019 tax return).
Look at Line 30 of Form 1040 on your 2020 return - that is where any additional stimulus credit due will appear.
