you can undo any scheduling operations:
$ svn add mistake.txt whoops
A mistake.txt
A whoops
A whoops/oopsie.c
$ svn revert mistake.txt whoops
Reverted mistake.txt
Reverted whoops
> svn add folder
A folder
A folder/file1.txt
A folder/folder2
A folder/folder2/file2.txt
A folder/folderToIgnore
A folder/folderToIgnore/fileToIgnore1.txt
A fileToIgnore2.txt