Revising a tax return

I completed my Federal and California state tax returns but have not filed them. I chose to mail my 

returns.  I have not mailed my returns yet. Now I need to change those returns because I put my RMD for my IRA in Section 4a of Form 1040-SR instead of under Additional Income Line 8 of Schedule 1.

Can I now change my returns to correct this error or do I need to file and make an amendment.