The order of lines in
/etc/sudoers is important.
The man page says:
When multiple entries match for a user, they are applied in order. Where there are
multiple matches, the last match is used (which is not necessarily the most specific
So, if you have the following usual line in your
%admin ALL=(ALL) ALL
and your user is part of the
admin group, you need to put the line in your question behind that line. Otherwise it will never be used, because the line for
%admin will always match instead.
In general, put the most specific lines (like those for single users and commands) at the end of the file.