Hi Pat!
Another way to get the layers smooth, in case you can't find binder clips big enough, is to use Duct Tape. First put your backing fabric face down & tape one side - using pieces of the duct tape - then smooth across & tape some more, then do the same on the other 2 sides. Next smooth your batting down & put the top on face up, smooth again, and tape the top the same way as the backing. Last step - baste! If you pin baste, put them in starting in the middle & working out, but DON'T close them yet. After you get it all pinned, carefully take the tape off & flip the whole sandwich over to check & make sure there aren't any puckers or folds. If it's OK, then flip it back & close all the pins, starting from close to you & working in, so you don't stick yourself! (I'm speaking from experience on that part! LOL)
Good Luck!
sue