Bari, QAYG is always an adventure -- at least for me. You absolutely have to trim your blocks. I've found it is necessary to baste my sandwich because no matter how well I pin, the backing always seems to go traveling. The method I've used is having the backing as sashing by folding it under. You do end up with a double sashing, but that's life. Sometimes using different backings can result in a more interesting look. Wishing you lots of luck!