The default configuration is defined in your application's web.config file here:
<configuration>
<connectionStrings>
<add name="ApplicationServices" connectionString="data source=SERVERNAME;Initial Catalog=aspnetdb;User Id=yourusername;Password=yourpassword" providerName="System.Data.SqlClient"/>
</connectionStrings>
<system.web>
<membership>
<providers>
<clear/>
<add name="AspNetSqlMembershipProvider" type="System.Web.Security.SqlMembershipProvider" connectionStringName="ApplicationServices" enablePasswordRetrieval="false" enablePasswordReset="true" requiresQuestionAndAnswer="false" requiresUniqueEmail="false" maxInvalidPasswordAttempts="5" minRequiredPasswordLength="4" minRequiredNonalphanumericCharacters="0" passwordAttemptWindow="10" applicationName="/"/>
</providers>
</membership>
The <connectionStrings> section will show you where you are connecting to the database, and the <membership> section shows how your membership provider is configured.
So, it sounds like you just need to change the connection string to point to the database that you set up (rather than the default aspnetdb database).