Ok, I love applique, so am excited about this. Can I make a couple of suggestions to the beginners that are trying applique for the first time? Only because I have learned from my own mistakes!!!
When cutting your background block, cut it about an inch or two larger than what the pattern calls for. When appliqueing the background will stretch a little and you will have a little to fudge. Then when finished, you can cut your block to the original size and then do the triangles on the corners.
Hope this helps