I just filed my 2020 tax return yesterday and realized that I forgot to add a 1099-R that I received from my old 401k custodian. The 2a box (taxable amount) is $0, and Box 7 says the letter "G". I can't amend it right now in TurboTax. Questions are below

1) Do I NEED to send a Amended tax return later on? What if I don't?

2)Based on your experience, is it highly likely that the IRS will send me a CP2000 in the future? 

I'm literally so scared that if they do send me the CP2000 and if I don't provide the necessary documentation (things that they accept), that something bad will happen

3) what do I need to provide in the CP2000 to ENSURE that everything is processed correctly?  Do I need to provide an account Statement from my new 401k custodian that proves that the money was indeed a Direct Rollover?

Any additional tips or advice would be greatly appreciated! 🙂