Help installing Surefire rail on Mossberg 500

[Hollywood!]

I am not sure what I am doing wrong, any help would be appriciated.
http://img.photobucket.com/albums/v639/Hydroponic2112/shoesting027.jpg
http://img.photobucket.com/albums/v639/Hydroponic2112/shoesting029.jpg

looks like the Fore-end tube isnt long enough??

First post woohoo:D