Help! Guinea pig cage!?

I've had my guinea pigs, Cleo & Penny for almost 3 months now. I did tons of research before getting them, so like most guinea pig owners, I put together a C&C cage out of storage grids. Its a spacious 2x4 with a 1x2 upper loft where their food, water & hay is. I didn't get enough coroplast, somebody had given me the wrong measurements when I went. I have coroplast for the bottom, and then out of my second sheet I cut it up to make only walls that I taped to the top loft, and 1 1/2 walls for my bottom that i also taped up. My guinea pigs put their hind ends right up to the cage grids and use the bathroom. I'm horrified. My carpet is only a year old and it's shag, so even vacuuming doesn't get all their droppings out! I'm at my wits end and dont know what to do. I've tried stick linoleum tiles to no avail. and I just don't have to money at the moment to purchase more coroplast and cut it up to tape to the cage walls again. What should I do?!?!