Yes, you will need to amend your return to report your 1099-R. This is because the IRS also receives a copy of your 1099-R and they will send you a CP2000 in the next year or two treating it as fully taxable unless you have reported it as not being taxable.
Amending your return is preferable to dealing with a CP2000. Here's how to Amend
My Return in TurboTax.
