Hi Judy,
Your backing should always be 3-5 or more inches bigger than your quilt top. You should also have your batting to be larger than your quilt top. If you need to you may have to add another border around the edge for this quilt's backing. It's best to spend the extra time to add another border to the backing, as this will make the quilting much easier.
There are several tutorials listed here and also some You Tube videos about basting a quilt both by pinning and by hand basting.
Have you pre-washed, ironed and starched your backing? Have you iron and starched your top? Have you laid your batting out to let the folds relax?
You don't mention how you plan on quilting the quilt. Are you machine quiting your self? Are you sending out to be long armed quilted?
Good luck with your quilting project and keep us updated on your progress.
Pam M