the backing should have a few extra inches all the way around larger than the quilt top- you place that down-smooth it without stretching it- then place the batting (also larger than the quilt top) smooth that over the backing- then place the top in the center with a few inches all the way around showing ---baste (either with pins or thread basting)
if you are using spray baste then you spray & layer--
secure the edges- then quilt as desired-
when the quilting is done the quilt is trimmed (squared up) so the edges are even for binding.