sew it together in pairs, then the pairs together into 2 halves, pinning at each match point & nesting the seams- press well (perhaps with starch as you complete each section- then sew the 2 halves together- i've had a couple which i actually matched my centers- pinned all the way across then started sewing in the center- out to one side- then turned over went back to center & sewed out to the other side. as long as your seams are nested, it is pressed well and you do it in sections it should go together nice & flat.