What is happening here?! Need help moving WordPress to sub

Hello! I’m trying to move my wordpress from the root of my site (theaquino.com) to a subdirectory (/WP13).

First I logged into my dash and changed the location of the files to /WP13. Then in FTP client, I moved all the wordpress files (-content, -admin, and -includes) from the root to the subfolder and then moved index.php from wp-admin folder to the root of the subdirectory (…also /WP13). First I tried copying the file and changing that one line in my index.php file (line 92):

‘include( ABSPATH . ‘wp-admin/admin-header.php’ );’

In my case, I added /WP13 in front, so ‘include( ABSPATH . ‘WP13/wp-admin/admin-header.php’ );’

….and that didn’t work (got an “error on line 10” notice). I fudged around (my next mistake…) and simply moved the index file (as opposed to copying) and now when you go to theaquino.com/WP13 I can see the public directory and all my WP files.

Is this fixable or have I royally ruined everything? Any help is much appreciated. I am, as you can see, inexperienced.

Thanks!