Can I get back into it to continue / modify? I was not finished with my return, just reviewing it.

[JohnR1]

Yes - if you are still in your return, you can click on My Account at the top of your screen and click Save & Sign Out.  This will save all of your progress.  In addition, TurboTax Online automatically saves as you work on your return.

Please see TurboTaxRobertaT's response to the question, "Can I Save My Progress?", below:

https://ttlc.intuit.com/replies/5389088