how do i remove the slash in url ,using htaccess

this my website mapping

--domain.com

------mainpage

---------index.php

my domain.com inside have a mainpage folder and inside the the folder have a index.php.

the url now

http://domain.com/mainpage/

the url i wanted(removing the slash)

http://domain.com/mainpage

.htaccess

Options +FollowSymLinks

RewriteEngine On

DirectorySlash Off

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_URI} !directory/(.*)$
RewriteCond %{REQUEST_URI} !(.*)$
RewriteRule ^(.*)$ http://domain.com/mainpage/$1 [R=301,L]