Don take a sheet of paper and fold under 1/4 inch seam then pin onto block either strip or even a triangle shape . Cut as you wish to make what you wish. Add little extra for seam or just incase. Then make a practise with fabric and sew onto one block cut to size.
You could put the block in the bottom right corner and just add new fabric on two sides making an off centre block. 101/2" block to 12" would need two pieces 2" in width .