Well a photo would help and remember if there is sashing it will take another 1/2 inch off those sides. So I say trim nothing at this point. Carefully pin the blocks together with the 1/4 inch seams or using a big basting stitch sew the parts together include the sashing do 4 blocks and see how it looks. Take a photo and post it. Then we can help with trimming if it needs it. As the blocks are 14 inches finished a tiny black border may not even show. Luann