If they wont take it back you may need to cut your losses and run (away from the store and never go back).
Get a small stock trough or large plastic tub to store the liverock in with a powerhead, heater and your junk skimmer. Then you can take your time figuring out a way to drill your tank for an overflow and sump or buy a new one.
While you're looking here are some more good book recommendations:
http://reefkeeping.com/issues/2008-01/tips/index.php
This was posted earlier today. Remora skimmer for $130. Its probably the smaller version... either way I wouldn't buy another one. Set up a drilled tank with a sump and you will have infinitely more options for skimmers.
http://www.canreef.com/vbulletin/sho...ghlight=remora