With that many pieces with points it is going to be difficult to not get some puckers in the background. Try sprit zing the block with water and iron face down on a plush surface. Sometimes a high pile towel with help to let you it on the background flat but allow the appliqué sit in the pile. Thus has helped me when there are quite a few appliqués sewn to the surface of a block.
I have the same problem sometimes with appliqué from pulling the thread a little too tight. I put my background in a locking embroidery hoop to avoid this problem.