The pre cut fabrics are cut using a laser system and aren't equal to cutting your own. Figure if each pre cut fabric is even just a couple of threads smaller, when trying to use in a large quilt, it could end up over an inch off. This would be compounded if you attempt to use both pre cut fabrics and some you cut. I know it's disappointing, but think of it as a learning experience. You'll probably have learned more from this than you would any other way. My heart goes out to you as we've all been there and would prefer not to repeat. Perhaps finish the quilt and donate to a homeless shelter or animal shelter. I've heard that some shelters have "ugly" quilt requests because the quilts aren't stolen!