Grids I bought the wrong grids.. advice?

Yes, it's too late too take them back. I accidentally bought the box with 5x5 & 8x8 (and the box was promptly torn into bits trying to get it open..) I was wondering since it's going to be a one level cage, can I cover up the first three or first two squares and be ok with using them? I have an idea on making a shower curtain with batting or fleece in the middle (using tape or sewing..) since I can't afford coroplast right now. My guinea pig was a craigslist rescue and has been stuck in a store cage until I'm able to get a c&c up and get a girlfriend for him. (Yes, One of them will be fixed!) So will they be ok like that?