Here's what I do:
*mark the middles of each piece
*tape the backing down, wrong side up
*line up the batting with the middle marks
*line up the top with the middle marks
*pin at the middle mark on the long side thru all layers
*fold back the batting and top to the pins at the middle
*spray baste the batting and smooth over the backing (I do in smaller sections, like 2-3 sections)
*spray the batting (also a small section at a time) and smooth the top over the batting
*once that half is complete, I do the same with the other half