A 2018 tax return completed in March of 2020 could only have been completed using the TurboTax 2018 desktop editions installed on a personal computer, not online.
If you used the desktop CD/Download editions installed on your computer, the only copy of your tax data file and any PDF's will be on the computer where the return was created. TurboTax does not store online any returns completed using the desktop editions.
Sadly if you did not keep a PDF of the return when you printed it to mail then you are out of luck. Until the IRS processes the return you will not have access to the transcript or copy. So you could reload the program again and complete the return again ... then you will have a copy.
You can get a return transcript from the IRS for free : http://www.irs.gov/Individuals/Get-Transcript
For a $50 fee you can get a copy of the return from the IRS: https://ttlc.intuit.com/questions/1901218-can-i-get-a-copy-of-my-tax-return-from-the-irs