Sounds like you are quilting it on your DSM? Suggest you glue base, sketch ahead of time, etc. Very unlikely that your LA quilter can get it perfectly lined up--think about rolling to towels together--at the end they don't come out the same--same principal with long arm and part of the reason that you need extra backing.
Either way, be sure that your back pieces are on the straight of grain-especially if you are using larger pieces, so that you don't get stretching that results in tucks,etc.