viola bridge question

I just got into viola today, coming from a violin/bas/guitar background. The bridge that came with my viola (see it here-http://www.amazon.com/gp/product/B004DK6G9W) is only the size of a violin bridge, and I can't seem to get it to stay in place. Do I need to find a new bridge, or am I just doing something wrong?

Thanks,
Matvei.