Fatal Error when Accessing Admin

I am not sure this is the right place to ask, but I did something very wrong on my blog… I upgraded to 2.3.3 this morning and I thought I followed the instructions correctly but I keep getting this error when I try and go into the admin side of my blog to follow the detailed instructions:

Fatal error: Call to undefined function: wp_admin_css() in /data/15/1/123/54/1449869/user/1558055/htdocs/wnyrealtor/wp-admin/admin-header.php on line 20

everything works on the front end, I cannot get back into the backend. Any suggestions?