Session question

I have a page that I use to log in to 'administor' club information. I
shouldn't be able to get to this page unless a session variable is set....
such as:

<cfif not structkeyexists(Session,"Username")>
<cflocation url="default2.cfm" addtoken="no">
</cfif>

But if I browse to the page that has this code at the top, I still get in,
even if its been a day since I logged in.

Why would this be occuring? And how can I prevent it, meaning how can I
force the <cflocation> to fire?

For some reason it thinks the session.Username is still active........