If this is made tube fashion, then the edges of the blocks are bias. Easy to stretch them while pressing or sewing. I think there is too much border fabric period. Measure and compare the block edges. If there is a slight difference--even 1/4 inch--that can translate to longer than necessary border and the resulting wavy-ness and all the blocking in the world will not help.
Go back to your pattern and determine what the correct measurement for each block should be. From that, calculate what the correct border length should be. Remove your border and cut to the correct length. Reapply, gently easing in the excess block fabric. I usually do this by marking the border at every intersection so that the fullness is evenly dispersed. If a block has really stretched, I have run a basting stitch along the edge and gently gathered in the extra fullness. It disappeared with the first wash.
Last edited by GingerK; 02-25-2017 at 06:04 AM.