I just sent in a 2017 Amended Tax return today (4/8/19) to claim two forgotten dedutions. I will receive $258 more back. Do I have to wait to file my 2018 taxes?

No, there is nothing in your amended tax return that impacts your 2018 tax return.

When you e-file your 2018 tax return and your AGI is requested, use the amount of your AGI on record with the IRS in October, 2018, not as shown on your amended tax return.