Connecting to ASPNETDB.MDF

I have added some collums to some of the tables in ASPNETDB.MDF and would like to display some of that data to my users on my website using the gridview.
I have added the following connection string to my web.config :
 
<connectionStrings>
    <remove name="LocalSqlServer" />
    <add name="LocalSqlServer" connectionString="data source=.\SQLEXPRESS;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|aspnetdb.mdf;User Instance=true" providerName="System.Data.SqlClient"/>
</connectionStrings>
 
When I add a gridview, ASPNETDB.MDF does not appear as a datasource.  I'm new to this, am I dumb?
Thanks
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