I am so sorry. My suggestion doesn't help now that it is finished but it may help for the next quilt. I have a mid-arm machine on my machine frame. (My frame is a B-line and it is the type that sits on the table.)
I bought a long length mirror and put it on the table under the quilt. I use a flashlight and inspect the underside of my quilt before I roll the quilt to the next row to be quilted.