A CP2057 means the IRS has more information on file for you than you reported.
https://www.irs.gov/individuals/understanding-your-cp2057-notice
The notice says what you failed to report. If you want to get a copy of your return to see if you really left off those items, your turbotax account has your return if you filed online. If you used the desktop program, only you have a copy of what you filed.
You can get your IRS transcript to see what they have on file for you. both in terms of the return you filed and your other income (but that's also in the notice). If the return you think you filed does not match the transcript, that might mean the IRS made an error, or it might mean you accidentally filed a return that was not complete. If there is income in your account history that does not belong to you (if your SSN was stolen and is being used by someone else) you can write a letter explaining that issue.
