I have created a page in Visual Force  to show a three column table how do I add this to show on the account page. I can see the visual force page in the page layout, but its still not showing three columns as I need to show
hours    date   description of activity         and normally it will only let you display two columns

My Test Code
<apex:page standardController="Account">
   <apex:pageBlock title="Hello {!$User.FirstName}!">
      You are viewing the {!account.name} account.
   </apex:pageBlock>

   <apex:pageBlock title="Contacts">

      <apex:pageBlockTable value="{!account.Contacts}" var="contact">
            <apex:column >
                        <apex:facet name="header">hours</apex:facet>
                        <apex:facet name="footer">column footer</apex:facet>
                        <apex:outputText value="{!account.owner.name}"/>
                </apex:column>
                    <apex:column >
                        <apex:facet name="header">description</apex:facet>
                        <apex:facet name="footer">column footer</apex:facet>
                        <apex:outputText value="{!account.owner.name}"/>
                </apex:column>
               <apex:column >
                        <apex:facet name="header">De Minimis</apex:facet>
                        <apex:facet name="footer">column footer</apex:facet>
                        <apex:outputText value="{!account.owner.name}"/>

                </apex:column>
      </apex:pageBlockTable>
   </apex:pageBlock>
</apex:page>

PS I am new to SF so please keep it simple.