I see the problem with the pattern. In step 4, the diagram doesn't show the blocks sewn together to form block sets in the proper configuration. and that incorrect configuration is used in the rest of the pattern. If you look at step 7, you will see that the polka dotted fabric pieces don't meet and form right angles as they do in the picture of the completed quilt. This messes up the design completely if you want the waterfall effect. If you just orient those pieces as they are in the first picture instead of as they are in the directions, I think you will be okay.
Jan's comments are also right on! No bias if you can avoid it.