To keep the back and front aligned I have some tricks that I use. First of all, I glue baste which means that I'm putting the batting down first and laying the backing or front on top of the batting. If you spray baste these tricks would work with that. With pin or thread basting where you are putting all three layers together at once you'd have to adjust this a bit.
After I've glued my batting to the back, I tape (with painter's tape) straws, chopsticks or something similar along a straight line on the right side of the backing. When I'm piecing with something obvious like a row of blocks the edge of the blocks is my straight line. This leaves a lump that I can feel through the batting. I lay the quilt top on top of the batting aligning a straight line on the top along the lump created by the straws/chopsticks etc. This way I know that both my top and back are straight to each other. I then glue the top to the batting by pulling it away in sections, gluing and then re-positioning.
I recently made a quilt where I put a border on the backing because I didn't have enough of the backing material. I wanted the border on the back to match a point on the front so when it was quilted it looked good from both sides. This technique worked like a charm. I couldn't match the edges because my batting and backing was larger than the top. It took a bit of work but the end result was dynamic and I'd do it again sometime.
Here are some examples of quilt backs I've done using this method.