You tape down the backing which is big then spray the batting on which is slightly smaller than backing. Now put on the top which means if you put very visible signs on the centre of the backing which is sticking out from the batting you should manage begin in the middle and outwards. You could put a mark in the centre of batting.
Be careful that you dont have too many seams laying together as it does affect your quilting flow. It is a big bump.
Good luck. Don't forget if spray basting is wrong you can also peel apart and try again.