IRS is only validating the source of the income on the return to ensure there is no fraud due to identity theft or erroneous amounts of tax withholding claimed.
I would wait until approx. April 10th and if you don't hear from IRS, then go ahead and amend the return and pay any additional tax due (if there is any) by 4-17-2018 to avoid any additional interest and penalties.
More detail on CP05 notice: https://www.irs.gov/individuals/understanding-your-cp05-notice
