domain mapping / multisite domain

Hello,
I'm running a blog at kentra24.novadic-kentron.nl. I have the domain kentra24.nl which I redirect to kentra24.novadic-kentron.nl. I would like the url in the address bar not to change to kentra24.novadic-kentron.nl and I have installed the Domain Mapping plugin. Somehow I cannot seem to get it to work. It keeps showing kentra24.novadic...

kind regards,
Ruud Verhoeven, ruud@leonard.nl