You need to ease the larger piece into the smaller one:
Pin the 2 ends.
Find the middle of the border & the quilt and pin those 2 together.
You now have 3 pins, dividing the quilt into 2 sections.
Find the center of the quilt and the border in each of the 2 sections and pin that together. Continue finding the centers of the border & quilt top in each unpinned section, and pin them together until all the fullness is absorbed. May take a lot of pins, but you will get there!