Include The Below given code

<reference name=”root”>
<action method=”setTemplate”><template>page/2columns-left.phtml</template></action>
</reference>

right under the default tag in in catalog.xml page

OR

Edit the page page.xml and replace the code

<block type=”page/html” name=”root” output=”toHtml” template=”page/3columns.phtml”>

With

<block type=”page/html” name=”root” output=”toHtml” template=”page/2columns-left.phtml”>