I have the pinnacle frame, so don't know how the two compares, but if you planned too closely on your backing to top ratio, there is one alternative, rarely considered on a quilt frame with three rails.
My daughter gave me a grandmother's flower garden to quilt; she had already basted all three layers together.
I was able to load the quilt on the take up rail, then attach it to the rail that is usually reserved for the backing.
WHile I quilted it, I kept one hand on the fabric to give added tension.
It worked pretty good, so you might consider loading all three layers on one rail to ensure the limited error range it sounds like you gave yourself is better within your control.