Fatal error on Upgrade

I copied core folder from 3.1.3 over the previous core from 2.8.34 (I didn't delete the 2.8.34 core folder, I renamed it, to enable a quick rollback if necessary)

I renamed (to disable it) the redactor folder used previously in editorial>addons>editors>plugins>editors ['editorial' is my name for the perch folder]

I am not using any other apps

when I attempted to sign in I got

Fatal error: Cannot redeclare perch_content() (previously declared in ../public_html/editorial/core/apps/content/runtime.php:18) in ../public_html/editorial/core/apps/content/runtime.php on line 42

Grateful for your help