What might help you get everything 'centered' vs 'lined up' so you can sandwich....try putting a really, really large safety pin (like diaper pin size - if anyone even remembers what THEY are!) in the CENTER of your backing. Find the center by folding in quarters. Follow the same process with your batting and then top. Place all the centering pins on top of one another. Then put a couple of pins through the whole sandwich to keep things in place so you can remove the pins from the backing and batting. Then begin your smoothing and basting process.
As long as your batting and backing are both larger than your quilt top, this should give you even distribution of the excess batting/backing around your top.