Good move on sending the email, but next time (for technique) send it at 7:55am instead of in the afternoon. HR usually works 8-5, so chances are when they check their email first thing in the morning yours will be on top of their inbox. Sending it in the afternoon after full days work will put your email between next weeks lunch menu and a dumb forward from a coworker.

Silly and petty, I know - but when trying to get a response every bit helps.