I need to see all the worksheets to make sure I filled everything out completely, so I want to look at the return before it's submitted. If I can fix it before it goes to IRS, I won't need to do a 1040-X later.
You should ALWAYS review the return carefully BEFORE filing the return and that option is part of the FILE tab process or in the Print Center ...
You can view your entire return or just your 1040 form before you e-file:
If you haven't efiled or mailed your return you can go back in and change anything you want. Do not click on Amend! Click on Add a State to let you back into your return.
From Tax Home (the first screen you see after you sign in), scroll down to Your tax returns & documents. You may have to select Show to open the drop down.
Select 2020, and then select Add a State (you're not actually adding a state, this is just the workaround).
Maybe you should consider using the Desktop program. Then you can see all the forms and enter directly into them. And the Desktop program has more features and other advantages over the Online version.