You're definitely not alone, or stupid! I'm lucky to have a quilting buddy (my mom) who can help me fix pretty much any mistake; it would feel a lot worse when I do things like that if I didn't have her.
I did learn a long time ago to make test blocks, and (almost) always do now. I have a set of fabric that I always use for tests... it never occurred to me until reading this thread, but I guess those test blocks will make a pretty quilt some day.
I don't know if this will help you, but I'd love it if you would post the fabric and cut sizes, to see if anyone can come up with a new pattern (or fix to your plan) using what you have. It would be a shame to waste all the time and effort you've put in so far, and someone might come up with something really cool.